I got lazy.
The arrow should be placed next to every rack tab.
there should be folder name text running vertical - either right side up text, or sideways and there should be some colour somewhere coloured the same as the user specified folder colour they painted it.
Hovering the mouse over the folder tab should give you pop-up infographic telling you which tracks are inside.
edit
This could also potentially enable the ability to have resizing capability of each folder section individually, so you could have the tracks in Drum Folder more narrow, and vocal tracks in Vocal Folder more wide… just resizing and or folding as you work from one thing onto the next to maximize space vs track title/insert/send readability, etc.