Show all subcategories on Categories module by default

Hey,

Really need your help to make this work. I want the sidebar category module to show all subcategories of all categories by default. Currently the module shows subcategories only when you click on a category and shows subcategories only of that category.

I'm just using the default module. I tried many different ways to get this work and nothing helped to achieve this. I know that I need to update files:
catalog/controller/module/category.php
catalog/view/theme/default/template/module/category.tpl

Thanks