Categories and child categories

[SideShowBob]

In the main category view \components\com_viertuemart\views\category\tmpl\default.php I would like it to display each category along with child categories i.e.

Category 1            Category 2
--Subcat 1             --Subcat 1
--Subcat 2             --Subcat 2
--Subcat 3             --Subcat 3

rather than just the top level categories

So it is essentially like a tree view.