Squarespace store preview pic shows nested navigation. But how??

As you can see, Squarespace store preview pic clearly shows nested navigation when you try to create a new store or a new category. But how do I actually achieve it? Surely, they wouldn't advertise it if it wasn't possible, otherwise it'd be considered false advertisement. Does anyone know how to nest store navigation just like Squarespace shows in the pic? Thanks.

Wow, had no idea. Thank you!