php把分类递归成数组

 function getTree($data, $pid){  

$tree = ''; 

foreach($data as $k=>$v)
  {
   if($v['parentid']==$pid)
   {
    
    //print_r($this->getTree($data, $v['linkageid']));
    $v['parentid'] = $this->getTree($data, $v['linkageid']);
   $tree[] = $v;
   }
  }
  return $tree;
 }