/**
* @return mixed
*/
public function allQuestions()
{
return Question::leftJoin(config('quiz.category_question_table'), config('quiz.questions_table') . '.id', '=', config('quiz.category_question_table') . '.question_id')->whereIn(config('quiz.category_question_table') . '.category_id', $this->getDescendantsAndSelf(['id'])->pluck(['id'])->all());
}
