Hi, not sure I'm understanding the issue - you're wondering how to have groups be subgroups?
To create a new subgroup, you can go to the Group and then Subgroups on the left panel.
If you want to make an existing group a subgroup of an existing group, then you can go to Create Subgroup > Existing Subgroup. Both elements shown in this screenshot:
If this helped you, please mark correct to help others : )