Drill-down to all children for all parents

[Trippple]

I'm working with IBM Cognos Analytics 11.1.x. In some cases I need to expand an dimension to all childrens in a report. For e.g.:

Before, only Level 1 is visible:
-CategoryFood
-CategoryDrinks

After, Level 2 is visible for each parent:
-CategoryFood
--Meat
--Sweets
--Vegetable
-CategoryDrinks
--Water
--Beer

It is easy to do this for only one of the Level1 Elements, but I don't know how to expand all Level 1 Elements to the childrens.

Thank's for you're help!