It never occured in my most pessimistic predictions we would only have one vote to decide two skilltrees, so I still cling to the hope there will be a second one.
My only problem with having two rounds of votes is that it could be the same majority that chooses both skill trees. In other words, more people would get
two skills they want and less people would get at least
one skill they want.
Edit:
Actually, I think a Single Transferable Vote better descibes the ideal method:
https://www.youtube.com/watch?v=l8XOZJkozfIPS: The bard would possibly be my last choice.