merge to datasources into one Dropdownlist

Hello,

 

I have 2 Datasources. One contains countries (countryCode, CountryName).  The other contains Cities (CountryCode, CitieName)

I want to add these datasources to a dropdownlist which must be sorted like

 USA
New York
Los Angeles
Miami
Italie
Rome
Venetie
SPain
Barcelona
Madrid

etc. etc. How can I retriev this? ...