Two levels for groups of users

Since groups getting more and more tuned and riched whit features.
Please consider making groups for groups of users.
Something like categories for groups.
This cloud be useful .
Something like this

Category of groups: Cities
And inside that there is each city: NY, Sarajevo, Tokyo etc.

Other Category of groups can be: Teams
And there is groups of users inside IT, Managmet, etc.

Grouping groups of users can be useful for users to easier navigate over groups, also it will be easier to self join in groups if we can display aggregates of groups to users.