求教无限分类的当前位置如何写，顶者有分！

/**
 +------------------------------------------------
 * 通用的树型类
 +------------------------------------------------
 * @author [email protected]
 +------------------------------------------------
 * @date 2010年11月23日10:09:31
 +------------------------------------------------
 */
class Tree
{
 
    /**
     +------------------------------------------------
     * 生成树型结构所需要的2维数组
     +------------------------------------------------
     * @author [email protected]
     +------------------------------------------------
     * @var Array
     */
    var $arr = array();
 
    /**
     +------------------------------------------------
     * 生成树型结构所需修饰符号，可以换成图片
     +------------------------------------------------
     * @author [email protected]
     +------------------------------------------------
     * @var Array
     */
    var $icon = array('分隔','分隔一','分隔二');
 
    /**
    * @access private
    */
    var $ret = '';
 
    /**
    * 构造函数，初始化类
    * @param array 2维数组，例如：
    * array(
    *      1 => array('id'=>'1','parentid'=>0,'name'=>'一级栏目一'),
    *      2 => array('id'=>'2','parentid'=>0,'name'=>'一级栏目二'),
    *      3 => array('id'=>'3','parentid'=>1,'name'=>'二级栏目一'),
    *      4 => array('id'=>'4','parentid'=>1,'name'=>'二级栏目二'),
    *      5 => array('id'=>'5','parentid'=>2,'name'=>'二级栏目三'),
    *      6 => array('id'=>'6','parentid'=>3,'name'=>'三级栏目一'),
    *      7 => array('id'=>'7','parentid'=>3,'name'=>'三级栏目二')
    *      )
    */
    function tree($arr=array())
    {
       $this->arr = $arr;
       $this->ret = '';
       return is_array($arr);
    }
 
    /**
    * 得到父级数组
    * @param int
    * @return array
    */
    function get_parent($myid)
    {
        $newarr = array();
        if(!isset($this->arr[$myid])) return false;
        $pid = $this->arr[$myid]['parentid'];
        $pid = $this->arr[$pid]['parentid'];
        if(is_array($this->arr))
        {
            foreach($this->arr as $id => $a)
            {
                if($a['parentid'] == $pid) $newarr[$id] = $a;
            }
        }
        return $newarr;
    }
 
    /**
    * 得到子级数组
    * @param int
    * @return array
    */
    function get_child($myid)
    {
        $a = $newarr = array();
        if(is_array($this->arr))
        {
            foreach($this->arr as $id => $a)
            {
                if($a['parentid'] == $myid) $newarr[$id] = $a;
            }