Database Schema - Groups, Subgroups, Users and Achievements

I asked something similar some days ago, but, something changed now. In the last question (here) I wanted to know how to make a database that could hold data for groups, users and achievements, but now I need to know how to do that, but also adding subgroups.

Here are the rules (change them if you think it's better):

• Groups can have multiple subgroups
• Sub-Groups can have multiple users
• Users can have multiple groups
• Users can have multiple subgroups
• Users can have multiple Achievements
• Every user is in the "Main" subgroup
• Achievements can have multiple subgroups

I have even more issues in this case because I don't know how to treat the subgroups and groups, and how I should relate achievements to the rest of the database.

I think i found a way to do this. I'll treat subgroups as normal groups (with achievements and users) and the group's table will be used to connect every subgroup in the same main group.