Taxonomy Exposed Filter - Single Dropdown Including Vocabulary and Term

I have a several vocabularies for countries. Within those vocabularies, I have terms which include cities.

Is it possible to created an exposed filter that includes the Vocabulary, and then the terms (but the user can select either or).

For example -

+ Belgium
- Brussels
- Antwerp
+ Germany
- Frankfurt
- Munich
- Cologne

The user can then select either Belgium, or Brussels. The view will then filter on either the appropriate vocabulary, or appropriate term.

Thanks.