Check for continuous binary tree in php

Php program for Check for continuous binary tree. Here more information.

<?php
/* 
  Php program for
  Check if binary tree is continuous tree
  Using recursion
*/
// Binary Tree Node
class TreeNode
{
	public $data;
	public $left;
	public $right;
	public	function __construct($data)
	{
		// Set node value
		$this->data = $data;
		$this->left = NULL;
		$this->right = NULL;
	}
}
class BinaryTree
{
	public $root;
	public	function __construct()
	{
		$this->root = NULL;
	}
	public	function absValue($num)
	{
		if ($num < 0)
		{
			return -$num;
		}
		return $num;
	}
	// Check tree is continuous or not
	public	function isContinuous($node)
	{
		if ($node != NULL)
		{
			if (($node->left != NULL && 
                 $this->absValue($node->data - $node->left->data) != 1) ||
                ($node->right != NULL && 
                 $this->absValue($node->data - $node->right->data) != 1))
			{
				// Case
				// When fail continuous tree rule
				return false;
			}
			if ($this->isContinuous($node->left) && 
                $this->isContinuous($node->right))
			{
				return true;
			}
			// When node value is not satisfied
			//  continuous tree properties
			return false;
		}
		return true;
	}
	public static
	function main($args)
	{
		// Create new tree
		$tree = new BinaryTree();
		/*  
		   Binary Tree
		   ------------
		       5
		     /   \
		    4     4
		   /     /  \
		  3     5    3
		   \
		    2
		        
		*/
		// Add tree node
		$tree->root = new TreeNode(5);
		$tree->root->left = new TreeNode(4);
		$tree->root->right = new TreeNode(4);
		$tree->root->left->left = new TreeNode(3);
		$tree->root->right->right = new TreeNode(3);
		$tree->root->right->left = new TreeNode(5);
		$tree->root->left->left->right = new TreeNode(2);
		if ($tree->isContinuous($tree->root) == true)
		{
			echo "Continuous Tree \n";
		}
		else
		{
			echo "Not Continuous Tree \n";
		}
		// Case 2
		/* 
		       5
		     /   \
		    4     4
		   /     /  \
		  3     5    3
		   \
		    1  <--- change value
		        
		*/
		$tree->root->left->left->right->data = 1;
		if ($tree->isContinuous($tree->root) == true)
		{
			echo "Continuous Tree \n";
		}
		else
		{
			echo "Not Continuous Tree \n";
		}
	}
}
BinaryTree::main(array());

Output

Continuous Tree
Not Continuous Tree