Drop down sub-categories… kinda?

(Apologies in advance. I’m having trouble coming up with the right word for what I want to do, which is why searching didn’t provide answers. lol)

I’m trying to clean up my sidebar and I was wondering if there’s a way to list the main categories in the sidebar with one of those little maximize/minimize “buttons” (usually look like plus and minus signs) so that when you click it, it will display/not display the sub-categories of each category individually?

I wish I had an example site to point to so you could see what I mean, but I don’t. Does anyone have any idea what I’m talking about? lol