SAB 8.6.6. MAC - HTML book list - tree structure

Would it be possible to make the roll-down menu of books in the PWA like the bookmarks in a PDF file. We have e.g, over 100 books and that is a very long list for a user, but it if we could first show 4 categories as we have them in the matrix in SAB for example like:

Bible Books OT
Bible Books NT

Just like they are defined in SAB when you set up each book.
Then when you click on e.g Bible Books OT you get the 39 books.

I hope that my explanation is clear enough!

Also this was posted long ago, but there was no response at that time. Maybe this time !

ALSO SAB 9.0 is missing this point in HTML and in PWA … as said this would be nice …
initially you would then say in my example the 5 entries and when you click on one of them it opens the books that are part of it …