App design how to organize views?

I'm developing an App in which users navigate through a tree structure using a lists, so the user sees:

root 1
root 2
root 3

After selecting one of those, they are on the next level of the tree structure and they see:

You are on root 2:
level 1
level 2
level 3

Navigating the structure is fine. My issue is that I also want a detail view for each item of the structure.
So right now I'm using tabs to show subitems in one tab and a detail view of the currently selected item on another tab. If you understand what I explained, you can guess this is probably not the best approach, as it feels a bit confusing/non-intuitive that both tabs behave as a detailview, one with subitems/levels and the other as an actual detail view.

The reason for navigating the tree structure like this instead of having a list of expandable items is that each item might have quite many subitems and scrolling much is not desirable. So the tree structure navigation solves that issue but creates anoter: I cannot anymore click an item and show its detailview.