forms – How to organize a multiple-selection list to select both users and groups, users who can have multiple groups?

So, for the moment, the system I'm developing has a multiple-selection list that ranks users by group. For example, the options in the selection list looked like this:

  • administrators
  • Finance team
    • Jordan Smith
    • Jeremiah Smith
    • Joe Smith

And the selected options were allowed for an entire category as well as for individual users, such as:
"Administrators", "Jordan Smith", "Joe Smith".

The problem is that the system has now evolved so users can have multiple groups. So, rather than just being a member of the directors or the finance team, they could be a member of both.

The selection list should always allow selection of individual users and entire groups. I could replicate individual users in multiple groups, so that they appear twice in the list, but I'm afraid this confronts the end user because if he used the input head, he would appear several times under different categories.