Kindle itself doesn’t support nested collections.
All it has is top level and just one level of collection.
I am not sure whether LS can do multiple sub-collections for you, but at least you can do a set of collection-subcollections as folders and then use folder hierarchy to build collections in LS.
What I mean is:
If you currently have Author1/ folder with Series1/, Series2/, etc subfolders inside, you can create a folder “Author1 - Series1”, “Author1 - Series2”, etc folders.
P. S. All in all I dropped that idea of moving folders/subfolders structure in one-to-one correspondence to Kindle, because the indexing is really fast (in case when all books have finished indexing) and you can find any book in a matter of a few seconds … to be able to dive into it for a good 2 weeks or more
