How to put only level 1 category in sidebar?

Hi,

I am using a complex category system involving three level deptshs.

E.g.

-Category 1 –> Sub-category 1 –> Sub-sub category 1.

It looks awful in my sidebar because it is a very long list. What I would like to do is to keep those categories intact because they are useful but only show level 1 on the sidebar. I’ll put the rest on a separate page.

How can I do this?

Thanks!