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;
}