We don’t know exactly why you’d want to do this. You can have multiple pages of apps within folders, so it’s not as if you’re exactly limited. Still, for anyone who wants to play around with things on iOS 7 beta, it’s possible to do this, maybe for fun … or something.
It doesn’t seem that this is an intended feature. It’s likely just a result of the operating system being an early beta release, and will probably be fixed in the near future. The folders work fine within each other.
The best way to do it is to watch the video above and follow it.