Can't seem to create subgroups

Hello. I'm new to Calibre so please excuse what I'm sure is an elementary question. It must have been asked and answered many times here but I can't find it.

I'm using the latest build (7.15) of Calibre on a Windows 10 laptop. I've set up a hierarchy structure and created a genre called "Cooking". When I try to create a subgroup under "Cooking" called "French", it appears instead as a new genre ("Cooking.French") separate from the genre "Cooking".

How do I create a subgroup under a genre? Any help is appreciated!