data.array

array
  'search_criteria_1' => 
    array
      'name' => string 'Search Criteria 1' (length=17)
      'choices' => 
        array
          0 => 
            array
              'element' => string 'Element 1' (length=9)
              'code' => string '001' (length=3)
              'is_selected' => boolean false
          1 => 
            array
              'element' => string 'Element 2' (length=9)
              'code' => string '002' (length=3)
              'is_selected' => boolean false
          2 => 
            array
              'element' => string 'Element 3' (length=9)
              'code' => string '003' (length=3)
              'is_selected' => boolean false

  'search_criteria_2' => 
    array
      'name' => string 'Search Criteria 2' (length=17)
      'choices' => 
        array
          0 => 
            array
              'element' => string 'Element 1' (length=9)
              'code' => string '101' (length=3)
              'is_selected' => boolean false
              'choices' => 
                array
                  0 => 
                    array
                      'element' => string 'Element 11' (length=10)
                      'code' => string '111' (length=3)
                      'is_selected' => boolean false
                  1 => 
                    array
                      'element' => string 'Element 12' (length=10)
                      'code' => string '112' (length=3)
                      'is_selected' => boolean false
   ...

GroupTreeSubscriber.php

<?php

namespace Examplecms\Bundle\ExampleCoreBundle\Form\EventListener;

use Examplecms\Bundle\ExampleCoreBundle\Form\GroupTreeType;

use Symfony\Component\Form\Event\DataEvent,
    Symfony\Component\Form\FormEvents,
    Symfony\Component\Form\FormFactoryInterface,
    Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Part of the Search Form Type.
 */
class GroupTreeSubscriber implements EventSubscriberInterface
{
    /**
     * @var FormFactoryInterface $factory
     */
    protected $factory;

    /**
     * @var array $options
     */
    protected $options;

    /**
     * The main constructor.
     * 
     * @param FormFactoryInterface $factory The form factory
     * @param array                $options The options
     */
    public function __construct(FormFactoryInterface $factory, array $options = array())
    {
        $defaults = array('searchCriteria' => null);

        $this->factory = $factory;
        $this->options = array_merge($defaults, $options);
    }

    /**
     * @return array
     */
    public static function getSubscribedEvents()
    {
        return array(FormEvents::PRE_SET_DATA => 'preSetData');
    }

    /**
     * Pre Set Data.
     * 
     * @param DataEvent $event The triggered event.
     *
     * @return type
     */
    public function preSetData(DataEvent $event)
    {
        $data = $event->getData();
        $form = $event->getForm();

        if (null === $data) {
            return;
        }

        if (isset($data['name'])) {
            $form->add($this->factory->createNamed('hidden', 'name', null, array(
                'label' => $data['name'],
            )));
        }

        if (isset($data['code']) && !isset($data['is_selected'])) {
            $data['is_selected'] = false;
        }

        if (isset($data['is_selected'])) {
            $form->add($this->factory->createNamed('checkbox', 'is_selected', null, array(
                'label'          => $data['element'],
                'required'       => false,
            )));
        }

        if (isset($data['choices']) && null !== $data['choices']) {
            $form->add($this->factory->createNamed('collection', 'choices', null, array(
                'type'           => new GroupTreeType(),
                'allow_add'      => true,
                'allow_delete'   => true,
                'prototype'      => true,
                'by_reference'   => false,
                'label'          => false,
            )));
        }
    }
}

GroupTreeType.php

<?php 
namespace Examplecms\Bundle\ExampleCoreBundle\Form;

use Examplecms\Bundle\ExampleCoreBundle\Form\EventListener\GroupTreeSubscriber;

use Symfony\Component\Form\AbstractType,
    Symfony\Component\Form\FormBuilder;

/**
 * A Search Element Type.
 */
class GroupTreeType extends AbstractType
{
    /**
     * Setup the form.
     * 
     * @param FormBuilder $builder The main form builder.
     * @param array       $options Options for the build
     */
    public function buildForm(FormBuilder $builder, array $options)
    {
        $subscriber = new GroupTreeSubscriber(
            $builder->getFormFactory(),
            array()
        );

        $builder->addEventSubscriber($subscriber);
    }

    /**
     * @param array $options
     * 
     * @return array
     */
    public function getDefaultOptions(array $options)
    {
      return array();
    }

    /**
     * @return string
     */
    public function getName()
    {
        return 'group_tree';
    }
}

SearchCriteriaSubscriber.php

<?php
namespace Examplecms\Bundle\ExampleCoreBundle\Form\EventListener;

use Examplecms\Bundle\ExampleCoreBundle\Form\SearchCriteriaType;

use Symfony\Component\Form\Event\DataEvent,
    Symfony\Component\Form\FormEvents,
    Symfony\Component\Form\FormFactoryInterface,
    Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Search Criteria Subscriber
 */
class SearchCriteriaSubscriber implements EventSubscriberInterface
{
    /**
     * @var FormFactoryInterface
     */
    protected $factory;

    /**
     * @var array
     */
    protected $options;

    /**
     * Main constructor.
     *
     * @param FormFactoryInterface $factory The form
     * @param array                $options The options
     */
    public function __construct(FormFactoryInterface $factory, array $options = array())
    {
        $defaults = array('searchCriteria' => null);

        $this->factory = $factory;
        $this->options = array_merge($defaults, $options);
    }

    /**
     * @return array
     */
    public static function getSubscribedEvents()
    {
        return array(FormEvents::PRE_SET_DATA => 'preSetData');
    }

    /**
     * Set data for the form.
     *
     * @param DataEvent $event
     */
    public function preSetData(DataEvent $event)
    {
        $data = $event->getData();
        $form = $event->getForm();

        if (null === $data) {
            return;
        }

        if (null === $data[$this->options['searchCriteria']]) {
            return;
        }

        $form->add($this->factory->createNamed(new searchCriteriaType(), $this->options['searchCriteria'], null, array()));
    }
}

SearchCriteriaType.php

<?php
namespace Examplecms\Bundle\ExampleCoreBundle\Form;

use Examplecms\Bundle\ExampleCoreBundle\Form\EventListener\GroupTreeSubscriber;

use Symfony\Component\Form\AbstractType,
    Symfony\Component\Form\FormBuilder;

use Examplecms\Bundle\ExampleCoreBundle\Form\EventListener\SearchSubscriber;

/**
 * Main search criteria Type.
 */
class SearchCriteriaType extends AbstractType
{
    /**
     * Setup the form.
     *
     * @param FormBuilder $builder The main form builder.
     * @param array       $options Options for the build
     */
    public function buildForm(FormBuilder $builder, array $options)
    {
        $subscriber = new GroupTreeSubscriber(
            $builder->getFormFactory(),
            array()
        );
        $builder->addEventSubscriber($subscriber);
    }

    /**
     * @param array $options
     *
     * @return array
     */
    public function getDefaultOptions(array $options)
    {
      return array();
    }

    /**
     * @return string
     */
    public function getName()
    {
        return 'search_criteria';
    }
}

SearchType.php

<?php
namespace Examplecms\Bundle\ExampleCoreBundle\Form;

use Symfony\Component\Form\AbstractType,
    Symfony\Component\Form\FormBuilder;

use Examplecms\Bundle\ExampleCoreBundle\Form\EventListener\SearchCriteriaSubscriber,
    Examplecms\Bundle\ExampleCoreBundle\Validator\Constraints as ExamplecmsAssert;

/**
 * Search form.
 */
class SearchType extends AbstractType
{
    /**
     * @param FormBuilder $builder The builder object
     * @param array       $options Its options
     */
    public function buildForm(FormBuilder $builder, array $options)
    {
      // Take into account search_criteria_1
      if ($options['search_criteria_1']) {
          $subscriber = new SearchCriteriaSubscriber(
              $builder->getFormFactory(),
              array('searchCriteria' => 'search_criteria_1')
          );
          $builder->addEventSubscriber($subscriber);
      }

      // Take into account search_criteria_2
      if ($options['search_criteria_2']) {
          $subscriber = new SearchCriteriaSubscriber(
              $builder->getFormFactory(),
              array('searchCriteria' => 'search_criteria_2')
          );
          $builder->addEventSubscriber($subscriber);
      }

      // Take into account search_criteria_3
      if ($options['search_criteria_3']) {
          $subscriber = new SearchCriteriaSubscriber(
              $builder->getFormFactory(),
              array('searchCriteria' => 'search_criteria_3')
          );
          $builder->addEventSubscriber($subscriber);
      }

      // Take into account search_criteria_4
      if ($options['search_criteria_4']) {
          $subscriber = new SearchCriteriaSubscriber(
              $builder->getFormFactory(),
              array('searchCriteria' => 'search_criteria_4')
          );
          $builder->addEventSubscriber($subscriber);
      }

      // ...
      }
    }

    /**
    * @param array $options
     *
    * @return array
    */
    public function getDefaultOptions(array $options)
    {
      return array(
        'search_criteria_1' => false,
        'search_criteria_2' => false,
        'search_criteria_3' => false,
        'search_criteria_4' => false,
        'search_criteria_5' => false,
        'search_criteria_6' => false,
        'search_criteria_7' => false,
        'search_criteria_8' => false,
        'search_criteria_9' => false,
        // ...
        'validation_constraint' => new ExamplecmsAssert\Search(),
      );
    }

    /**
     * @return string The name of the form
     */
    public function getName()
    {
      return 'search';
    }
}