PHP 生成子孙树

function makeTree($data)
{

    $res = [];
    $tree = [];

    // 整理数组
    foreach ($data as $key => $vo) {
        $res[$vo['id']] = $vo;
    }
    unset($data);

    // 查询子孙
    foreach ($res as $key => $vo) {
        if ($vo['pid'] != 0) {
            $res[$vo['pid']]['child'][] = &$res[$key];
        }
    }

    // 去除杂质
    foreach ($res as $key => $vo) {
        if ($vo['pid'] == 0) {
            $tree[] = $vo;
        }
    }
    unset($res);

    return $tree;
}