Categories view aggregated

Let’s say, you organized your categories like this

CAT1
|_ CAT.1.1
|_ CAT.1.2
|_ CAT.1.3
CAT2
|_ CAT.2.1
|_ CAT.2.2
|_ CAT.2.3

Is it possible that you enable only the main categories links on the left side bar
CAT1
CAT2

And by clicking on e.g. CAT1 in the side bar the user is directed on a page where he only does see an overview of the subcategories linked

CAT.1.1
CAT.1.2
CAT.1.3

But not it’s contents/threads?