How to create question pool within the question pool

Hi, i am using captivate 8 to create my quiz.

I would like to create the sub-question pool within the question pool.

For example, I have question pool 1 & question pool 2. Inside the question pool 2, I would like to have question poo1 2A and question pool 2B.

Please refer to my attached image.

I can't find any setting inside the captivate quiz, and even i have created the branching, the problem is it it will keep on going to the question pool 2A.

Appreciate if someone can give me the solution. Thanks!