如何在laravel-mongodb上设置删除级联？ （Laravel 5.3）

My delete method on controller is like this :

public function delete($id)
{
    MessageThread::destroy($id);
}

When the code executed, It success delete a record by id

But, the data on child table not deleted

Seems it must set on delete cascade

How can I set it?

I get the reference from here : https://github.com/jenssegers/laravel-mongodb