I only want to to list parent categories

Hi,

I have a large number of categories (business directory) currently my site shows all parent categories and child categories (i’ve created a child category per business) e.g.
accountants
-an accountant ltd
-ernst & young
beautician etc

I would like only to list parent categories e.g. accountant, beautician and when you click on the category each business (child category)is shown so you could then choose which business to click on. Each child category would hold a single post.

I’m not sure if there is a way of doing it within current wp or do I need plug in?

Can anyone help?

Regards

Carol