$this->funF([$v['id']], $lists);

private function funF($list, &$rest)
{
    foreach ($list as $item) {
        $rest[] = $item;
        $this->funF($this->fun($item), $rest);
    }
}

public function fun($ids)
{
    return User::where("invite_id", $ids)
        ->column('id') ?: [];

}