Many thanks, for starting this thread .. I've looking for a way to display Multi-Level Help Topics, for a while; and I have even put in a feature request for the same on Github..
The mod that sosamv was awesome, but worked only up until 1.10, I think .. It would be great, if this worked for the latest version too.. Also, it seems that the author has not been active on this forum post 2017
There is, however, a paid plugin called CartMega Superlists that'll help you achieve Multi-Level Dynamic List-Boxes.. However, it's not entire Plug-n-Play, and would require some knowledge of SQL & PHP .. You'll find it here..
Anyway, keep us updated, if you make any progress on sosamv's'* mod..