php无限分类的类

<?php
/**
 by lenush;
 */
class Tree
{
    var $data    = array();
    var $child    = array(-1=>array());
    var $layer    = array(-1=>-1);
    var $parent    = array();
    function Tree ($value)
    {
        $this->setNode(0, -1, $value);
    } // end func
    function setNode ($id, $parent, $value)
    {
        $parent = $parent?$parent:0;
        $this->data[$id]            = $value;
        $this->child[$id]            = array();
        $this->child[$parent][]        = $id;
        $this->parent[$id]            = $parent;
        if (!isset($this->layer[$parent]))
        {
            $this->layer[$id] = 0;
        }
        else
        {
            $this->layer[$id] = $this->layer[$parent] + 1;
        }
    } // end func
    function getList (&$tree, $root= 0)
    {
        foreach ($this->child[$root] as $key=>$id)
        {