树形结构

 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;
    }