Create comment hierarchy from array

Comment.php

<?php

class Comment
{

    /**
     * @var integer
     */
    private $id;

    /**
     * @var \DateTime
     */
    private $createDatetime;

    /**
     * @var string
     */
    private $value;

    /**
     * @var string
     */
    private $model;

    /**
     * @var integer
     */
    private $modelId;

    /**
     * @var array
     */
    private $children;

    /**
     * @var Comment
     */
    private $parent;

    /**
     * Get id
     *
     * @return integer
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Set createDatetime
     *
     * @param \DateTime $createDatetime
     *
     * @return Comment
     */
    public function setCreateDatetime($createDatetime)
    {
        $this->createDatetime = $createDatetime;

        return $this;
    }

    /**
     * Get createDatetime
     *
     * @return \DateTime
     */
    public function getCreateDatetime()
    {
        return $this->createDatetime;
    }

    /**
     * Set value
     *
     * @param string $value
     *
     * @return Comment
     */
    public function setValue($value)
    {
        $this->value = $value;

        return $this;
    }

    /**
     * Get value
     *
     * @return string
     */
    public function getValue()
    {
        return $this->value;
    }

    /**
     * Set model
     *
     * @param string $model
     *
     * @return Comment
     */
    public function setModel($model)
    {
        $this->model = $model;

        return $this;
    }

    /**
     * Get model
     *
     * @return string
     */
    public function getModel()
    {
        return $this->model;
    }

    /**
     * Set modelId
     *
     * @param integer $modelId
     *
     * @return Comment
     */
    public function setModelId($modelId)
    {
        $this->modelId = $modelId;

        return $this;
    }

    /**
     * Get modelId
     *
     * @return integer
     */
    public function getModelId()
    {
        return $this->modelId;
    }

    public function addChild(\SD\TaskBundle\Entity\Comment $child)
    {
        $this->children[] = $child;
        $child->setParent($this);
    }

    public function removeChildren(Comment $children)
    {
        $this->children->removeElement($children);
    }

    /**
     * Get children
     *
     * @return array
     */
    public function getChildren()
    {
        return $this->children;
    }

    public function setParent(Comment $parent = null)
    {
        $this->parent = $parent;

        return $this;
    }

    /**
     * Get parent
     *
     * @return Comment
     */
    public function getParent()
    {
        return $this->parent;
    }

}

Hierarchy.php

<?php

class CommentRepository extends EntityRepository
{
    public function getTreeStructure($model, $modelId)
    {
        $nodes = $this->findBy([
            'model' => $model,
            'modelId' => $modelId
        ]);

        $nodesWithoutParent = [];

        /** @var Comment $node */
        foreach ($nodes as &$node) {
            $node->getChildren()->clear();

            if (is_null($node->getParent())) {
                $nodesWithoutParent[] = $node;
            }
        }

        foreach ($nodes as $key => &$node) {
            /** @var Comment $parent */
            foreach ($nodes as &$parent) {
                if ($parent === $node->getParent()) {
                    $parent->addChild($node);
                }
            }
        }

        return $nodesWithoutParent;
    }
}