Using Nested Categories?

I am trying to setup nested categories in Calibre. I used this guide:

https://team3eng577.wordpress.com/ca...ries-and-tags/

This works well but then I cannot work out how I am supposed to add books to the sub categories. There just doesn't seem to be an option and drag and drop doesn't work.

So I then found this guide which does it in a very different way:

https://manual.calibre-ebook.com/sub_groups.html

This seems to work okay but it is a bit of a pain the way you have to manually enter new sub categories as category.subcat.subcat.{etc}
Also I prefer the first method as you can change the icon of each sub category whereas the second method you don't seem to be able to do this.


Which is the preferred method? Also, how do you add books to the first method?

The second method also explains at the end how to maintain these groups when saving to device or disk which I would definitely want to do. Can the same be achieved with the first method?