Flame Graph doesn't tell its scope

1. Show some recorded data in the Flame Graph view.
2. Double click one of the red boxes.
   This box will be expanded to be the new scope of the view and everything above it will be zoomed accordingly.
   Now it's neither obvious that the current view is zoomed to this scope, nor is there an obvious way to zoom out again (as double-clicking the empty space does).

It would be good to have something like a vertical bread crumb navigation that lets the user go back to the full scope step by step.