Hi,
Set is like a search, it’s not what you want.
Collection is like a unique folder or a box where you put what you want.
It can meet the need : you can add your chapter, tag or categorize them.
And you can add this collection to the sidebar (the view is simple at present, but perhaps one day it will be possible to customize it to display the category, for example).
Here : a collection, with chapter tagged with book name + collection added to the sidebar
If you prefer a tree view (like folders), you can create a page and create other page in it.
You can customize with icon, preview, what you can.
Personally, I’d do it this way.
Here : a page containing all my books (one with preview layout for exemple) , each of them containing their own chapter + the page added to the sidebar with tree view
And if you want to see all your chapter in one view, you can also add them to a collection.
Or simply “search” them : it’s a job for a set
Here : a basic set filtered by object type = page... you have to filter differently, pehaps tagging all you chapter, pehaps creating object type like "Chapter"
We can’t see “parent” here for now (there is a FR for that), too bad it would allow you to see the chapters + the book that contains them without cheating (give the name of the book in the chapter, as some do here).