the category menu

Hi, I have parents and children categories set up. the parent category serves a label for the “set” of children categories. it is really not used to have post in itself. however, if there is no post saved at parent category level, the parant category won’t show on category menu list. for example:

I want to have this menu:

Drug
    Inhalants
       Definition
       Recent Articles
       Pictures

This will need a grandparent category, a parent category and three children categories. How to let them show up without saving a post to each of them?

Thank you.