gistfile1.php

<?php
echo '<pre>';

class node
{
  var $name = NULL;
  var $left = NULL;
  var $right = NULL;
  var $content = NULL;

  public function __construct( $name )
  {
    $this->name = $name;
  }
}

$food = new node('Food');
$fruit = new node('Fruit');
$meat = new node('Meat');
$red = new node('Red');
$yellow = new node('Yellow');
$strawberry = new node('Strawberry');
$cherry = new node('Cherry');
$banana = new node('Banana');
$lemon = new node('Lemon');
$orange = new node('Orange');
$tangerine = new node('Tangerine');
$beef = new node('Beef');
$pork = new node('Pork');
$maraschino = new node('Maraschino');

$meat->content = array($beef, $pork);
$cherry->content = array($maraschino);
$red->content = array($strawberry, $cherry);
$yellow->content = array($banana, $lemon);
$orange->content = array($tangerine);
$fruit->content = array($red, $yellow, $orange);
$food->content = array($fruit, $meat);


function build_it( $pages, $left = 1, $right = null)
{
	if( is_array( $pages->content ) )
	{
  	$pages->left = $left;
	  foreach( $pages->content as $page )
 	  {
 	    $left++;
  		$right = build_it( &$page, &$left);
	  }
	  $pages->right = ++$right;
	}
	else
	{
	  $pages->left = $left;
	  $pages->right = ++$left;
	  return $pages->right;
	}

	$left++;
	return $right;
}

build_it( &$food );

print_r($food);