无限分级

function getTree($items) {
        foreach($items as $value){
            $value['son'] =array();
            $new_address[$value['id']] = $value;
        }
        foreach($new_address as &$value){
            if($value['pid'] !=0){
                $new_address[$value['pid']]['son'][] = &$value;
            }else{
                $res_address[$value['id']] = &$value;
            }
        }
        return $res_address;
    }