With the My Groups element on a Portal page, you can choose to display all top-level tiers, or one top-level tier per My Groups element.
The My Groups element defaults to no selection, which results in all Groups (which have Group Spaces enabled) being displayed regardless of which top-level tier they are in.
If you specify a particular group to display however, the My Groups element will only display Groups from that same tier. You can select which Group or Tier you would like to display within the My Groups element by clicking on the pencil icon for that element from within the Unpublished tab.
It is possible to add multiple My Groups elements to a Portal page to display selected Groups from different tiers.