public   function   get_tree(){        //递归遍历数组;        $items=[];        foreach($position as $k=>$v){                $items[$v['id']]=$v;        }        $tree=[];        foreach($items as $k=>$v){                if($v['pid'] && isset($items[$v['pid']])){                $items[$v['pid']]['children'][]=&$items[$k];            }else{                $items[$k]['cid']=$company_id;                $tree[]=&$items[$k];            }        }        return  $tree;    }