使用遞歸函數，不過我寫這種方法空間複雜度沒有得到優化，忘記以前的寫法了

private function getTreeList($data, $pid = 0)
    {
        $resultarr = array();
        foreach ($data as $teamdata) {
            if ($teamdata['pid'] == $pid) {
                $team_data = $teamdata;
                $children_data = $this->getTreeList($data, $teamdata['id']);
                $team_data['children'] = $children_data;
                $resultarr[] = $team_data;
            }
        }
        return $resultarr;
    }

用递归来循环出一个数组

public function gettree($items, $parent_id = 'parent_id', $id = 'id'){
    $tree = array(); //格式化好的树
    if(empty($items)){
        return $tree;
    }
    foreach ($items as $item){
        if (isset($items[$item[$parent_id]])){
            $items[$item[$parent_id]]['son'][] = &$items[$item[$id]];
        }else{
            $tree[] = &$items[$item[$id]];
        }
    }
    return $tree;

}