binarytree.php

<?php

class TreeNode
{
    public $value;
    
    public $left;
    
    public $right;
    
    public function __construct($item) 
    {
        $this->value = $item;
    }
    
    public function dump()
    {
        
        if ($this->left !== null) {
            $this->left->dump();
        }
        
        var_dump($this->value);
        
        if ($this->right !== null) {
            $this->right->dump();
        }
        
        
    }
}

class Tree
{
    protected $root;
    
    public function isEmpty()
    {
        return $this->root === null;
    }
    
    public function insert($item)
    {
        $node = new TreeNode($item);
        
        if ($this->isEmpty()) {
            $this->root = $node;
        } else {
            $this->insertNode($node, $this->root);
        }
    }
    
    public function traverse()
    {
        $this->root->dump();
    }
    
    protected function insertNode($node, &$subtree)
    {
        if ($subtree === null) {
            $subtree = $node;
        } else {
            if ($node->value > $subtree->value) {
                $this->insertNode($node, $subtree->right);
            } elseif ($node->value < $subtree->value) {
                $this->insertNode($node, $subtree->left);
            } else {
                //no dupes
            }
        }
    }
}

$tree = new Tree;

$tree->insert(3);
$tree->insert(8);
$tree->insert(5);
$tree->insert(4);
$tree->insert(2);
$tree->insert(7);
$tree->insert(6);
$tree->insert(1);

$tree->traverse();

print_r($tree);