Just found another thread...I DID search first, but didn’t see that one.  Never mind. :)

I’ll add this in case anyone else sees it. While there is currently no nested collection option, you can add groups of collections to a Guideline if you have the Brand guidelines module. You can choose how many assets are displayed, and how they can be downloaded.

Thanks!  That’s what I found.  Now I just have to find out if we have that module.

As we have so many Collections, I’ve got round this by listing the various collections on our home page news feature type article. 

Oh great idea!  Thanks for that suggestion.