Hierarchical projects


I want to organize the projects in a hierarchical way and control its membership. Using Gitlab groups I am able to organize the projects hierarchically, but the problem is that I cant find a way to limit the membership to sub-groups. As an example consider the following project hierarchy (and who should have permission)

-> sub math1 // user1, user2
-> sub math2 //user 1

-> sub science1 //user3, user1
-> sub science //user 2

I can assign user1, and user2 to mathproject group, but then, both of the will have access to sub math2 project. I only want user1 to have access to it (and not user2)

How can I achieve the same?

I was looking for the same capability, but I came to the conclusion that all projects in a group share the same access permissions for each user. This is very unfortunate.