When adding a subcategory (like Hotels) to a category (like Accommodation), you can add the subcategory to either Group 0 or Group 1.

For example on this page we have added the Bed and Breakfast and the Hotels subcategories to Group 0 and the Forest region and the River region to Group 1.

As you can see on the right hand side of this page, that automatically groups the subcategories together depending on the group chosen.

You can also link listings in one category to another category, so they will be listed in both categories. For example, you can link a Bed and Breakfast listing to the Forest region category, so visitors can browse either the Bed and Breakfast listings or the list of Forest region accommodation.