If someone tells you he knows for a fact that Christmas trees came from some pagan religion, he's lying.
If someone tells you he knows for a fact that Christmas trees were started by Christians with no pagan connections, he's lying too.
Personally, I find it extremely unlikely that the Christmas tree tradition was invented in the 16th century out of whole cloth, but the unfortunate fact is that nobody knows who started it nor why. There is no solid historical evidence on the matter.
Of course, if just a fraction of the resources that go into Christmas were applied to keeping the holidays that we know beyond any doubt that God gave to mankind, the question would become purely academic.
(If someone does manage to find a primary source on the origin of Christmas trees, I'd love to see it! I will happily retract this statement.)
