Fighting the xml-s, but i am wining the battle 
I can add totaly new cityset without creating a new techtree!!!
Solution: define a new race, add it as prereq to the building, add prereq: race type men to the original buildings and edit the files where the >men< is required. Believe me this method is easier than creating a totaly new techtree. And with this prereq-s you can edit the techtree either.
For example the tech tree of my nordic nation will be very similar to the kingdoms, but instead of irrigation they have thermal irrigation.
Picture next time, going to sleep.