无限极分类（用于一级二级展示的方法）

 public function tree($data,$parent_id = 0,$leave = 0)
    {
        static $tree = array();
        foreach($data as $k => $v){
            if($v[‘parent_id‘] == $parent_id){
                $v[‘leave‘] = $leave;
                $tree[] = $v;
                $this->tree($data,$v[‘cat_id‘],$leave+1);
            }
        }
        return $tree;
    }