There's a passage in Tacitus about the Germans revering trees, this would be referring to 9AD.
You'll have to cite the exact passage so we can have confirmation, but that seems about a century early, as Tacitus wrote around the year 100 AD, unless he was specifically referring to things a century ago.
However, this is where we run into a major problem with the whole "this thing in Christmas is like this thing pagans did way back when" arguments. If the claim is it comes from paganism, then we need evidence that:
1) Pagans actually did engage in this practice (you'd be surprised how people just make up; this is why it is critical to cite primary sources)
2) They did so in close enough proximity to Christians that Christians could have been influenced
3) Pagans did so close enough to the beginning of the applicable Christian practice that influence was possible
What a lot of people don't realize is that a lot, perhaps even the majority, of Christmas customs we have are actually recent developments of the last few centuries. By that point, paganism had gone extinct in Europe and had been so for centuries upon centuries. So whatever ancient people did that might have resembled Christmas customs (if they
did do them, again a whole lot of false claims get made), it couldn't have influenced the development of those Christmas customs because there's far too big a gap of time between them.
So let's analyze this claim of yours according to these 3 requirements. You haven't demonstrated #1 because all you've done is given a vague reference to Tacitus. #2 is not clear either; Germans were
outside of the Roman Empire. Were Germans, if they were doing this in the days of Tacitus, still doing it at the time when there was stronger Christian contact? And #3 is flat out; Christmas trees started around the 16th century AD, by which point those pagan practices had completely ceased long ago. Even then, I don't think Christmas trees actually got popular until several centuries later. All three of these need to be true for the "pagan influence" idea to even be
possible, so failure to meet any of them means the whole thing collapses. Since #3 fails irrespective of #1 and #2, this argument is therefore without merit.
A far more plausible origin of the Christmas tree, as the Oxford Handbook of Christmas says in chapter 22, is:
“The Christmas tree tradition most likely developed from a combination of medieval liturgical traditions and guild patronage to local communities, which over time were transformed into a private practice beginning in the sixteenth century. In the medieval period, many people could not read and write, so plays were a way to communicate biblical stories.
In that time, a Paradise Tree was set up for plays to represent the Tree of the Knowledge mentioned in Genesis 2:9. The actor playing Adam would later parade through the streets of the town with the tree. The tree symbolized humanity’s downfall but also represented the tree of the cross, which would become the salvation of all people. Medieval tradition even claimed that Adam had taken a branch from the Tree of Knowledge and Jesus’ cross was made from that tree.
The trees were decorated with apples, representing the Fall of humankind, while round pastry wafers on the tree symbolized the Eucharistic host as the path to salvation. The plays were performed on 24 December, which was the feast day for Adam and Eve. The display of the Paradise Tree was meant to symbolize the Garden of Eden where they lived. The liturgical calendar placed their feast day here to remind Christians that Jesus’ birth was a conduit of salvation allowing humanity to return to its perfect state in the Garden.”
It went into some more detail, but this was the only portion I have easily available to post (it was so useful I made sure to jot it down for future use). Still, it is fairly easy to see how a practice of decorating a tree on December 24 could easily have caused tree decoration to spread to the very next day. However, this custom emerged from a
biblical story, and while earlier than Christmas trees, again comes too late to have had plausible influence from ancient paganism.
The Druids also decorated trees and put up Miseltoe, in the centuries BC. Ancient Pagan customs.
Unlike before, where you at least cited a vague source, here you offer none (thus we cannot say that requirement #1 has been proven). But let us suppose this is indeed the case. As noted above, we run into the major problem that tree decoration on Christmas developed far too late for this to have had any impact (failing requirement #3). As for mistletoe, the "kissing under the mistletoe" tradition cannot, as far as I can tell, be traced back any farther than the 18th century, so we run afoul of #3 again by citing a tradition that developed so long after any pagans might have done it that no connection is really possible.
