[Plugin: Taxonomy Drill-Down] How to add TAGS as a taxonomy on widget?

I’ve activated Taxonomy Drill Down 1.4. I was surprised to see that on the widget there is only one taxonomy listed: Category Groups. I was expecting to see Post Tags listed as it is on the example screenshot.

This is what my widget looks like:
https://i940.photobucket.com/albums/ad249/webmomma/taxonomywidget.png

I want my users to be able to search posts by selecting multiple tags at once. How do I add Post Tags as a taxonomy on the widget?

Thanks!