How to create virtual library for comic files (with different extensions)?

I'm trying to figure out how to create a virtual library for files ending in .cbz AND .cbr. But for the life of me I can't see how to do it.

I can create a virtual library for just .cbr or just .cbz, but not both.

Is there a way to do this? Sorry if it's a stupid question, I really have tried to figure this out on my own.
Any help would be greatly appreciated -- thanks in advance!