Detect leaf nodes of threaded BST in php

Php program for Detect leaf nodes in threaded BST. Here more solutions.

<?php
// Php program for
// Print leaf node in Threaded BST
class TreeNode
{
	public $data;
	public $left;
	public $right;
	public	function __construct($data, $left, $right)
	{
		$this->data = $data;
		$this->left = $left;
		$this->right = $right;
	}
}
class BinarySearchTree
{
	public $root;
	public	function __construct()
	{
		$this->root = NULL;
	}
	// Added node in Threaded BST
	function addNode($node, $x, $y, $data)
	{
		if ($node != NULL)
		{
			if ($node->data >= $data)
			{
				if ($node->left == $x)
				{
					$node->left = new TreeNode($data, $x, $node);
				}
				else
				{
					$node->left = $this->addNode(
                      $node->left, 
                      $x, 
                      $node, 
                      $data);
				}
			}
			else if ($node->data < $data)
			{
				if ($node->right == $y)
				{
					$node->right = new TreeNode(
                      $data, 
                      $node, 
                      $y);
				}
				else
				{
					$node->right = $this->addNode(
                      $node->right, 
                      $node, 
                      $y, 
                      $data);
				}
			}
			return $node;
		}
		else
		{
			return new TreeNode($data, $x, $y);
		}
	}
	// Adding a new node in binary search tree
	public	function add($data)
	{
		$this->root = $this->addNode($this->root, NULL, NULL, $data);
	}
	// Print all leaf node in Threaded BST
	public	function leafNode($node, $x, $y)
	{
		if ($node != NULL)
		{
			if ($node->left == $x && $node->right == $y)
			{
				// This is a leaf node Then print
				echo "  ".($node->data);
				return;
			}
			if ($node->left != $x)
			{
				// Visit left child
				$this->leafNode($node->left, $x, $node);
			}
			if ($node->right != $y)
			{
				// Visit right child
				$this->leafNode($node->right, $node, $y);
			}
		}
	}
	public static function main()
	{
		$tree = new BinarySearchTree();
		// Add nodes in binary search tree
		/*
		            5
		           / \
		          /   \
		         /     \
		        3       9
		       / \     / \
		      1   4   8   11
		     / \     /      \
		   -3   2   7        12
		        
		*/
		$tree->add(5);
		$tree->add(3);
		$tree->add(9);
		$tree->add(1);
		$tree->add(4);
		$tree->add(8);
		$tree->add(11);
		$tree->add(-3);
		$tree->add(2);
		$tree->add(7);
		$tree->add(12);
		// Test
		$tree->leafNode($tree->root, NULL, NULL);
	}
}
BinarySearchTree::main();

Output

  -3  2  4  7  12