To create data hierarchies in a pivot right click on the Pivot title and select Edit Data Hierarchies

 

The Data Hierarchies editor will open allow you to add dimensions under the selected dimension:

Now select a dimension on left panel and drag & drop dimensions from the Data Browser under the dimension element on the right panel:

 

Click on OK and the Pivot Hierarchy is set. Now you can hover the dimension header or any member on the Pivot and a quick menu will pop up indicates you can Drill Down, Drill Up or Expand and Collapse:

Result After Expanding the product dimension:

 

Drill Down:

 

Result After Drill Down:

Note: hovering the information icon will show the user the drilled down member in the Background Section