From AKBAN-wiki, the Martial Arts Database

category tree is installed

Here are several examples of usage

Writing <categorytree> Budo Ninjutsu techniques </categorytree> gives the root category, you can press the "+" to expand any one on the list, try, for example, the "Blocks" since it has a sub category... :

Writing <categorytree hideroot=on> Budo Ninjutsu techniques </categorytree> gives the subcategories with out the root:

Writing <categorytree mode=pages> Budo Ninjutsu techniques </categorytree> gives all pages, try pressing the "+":