However, even if we grant that they are followers of a guy named Jesus, whom we are told was called "the Christ", it's not clear how they associate this holiday with anything taught by Jesus. Surely Jesus knew his own birthday, and presumably it would have been a trivial matter to record it, or to reveal it at some later date. Surely, if he wanted them to celebrate his birthday on a yearly basis he could have mentioned it to his followers or talked about it in the Gospels. How is it that Jesus missed talking about what many Christians will tell you is the most important day of the year in the Christian calendar?
Furthermore, not only does Jesus fail to talk about any kind of date for his birth that is to be celebrated, but it is not at all clear how symbols like evergreens or decorated Christmas trees would have anything to do with him. Furthermore, despite some ridiculous, transparently revisionistic myths attempting to claim that tree decorating customs were invented by Christians, it is quite clear that the evergreens had special significance to various pagans, who were animists and nature worshippers, believing that special spirits and magic powers resided in trees. The Greeks, Romans, Scandinavians, and even Egyptians among others, decorated with green tree matter, during the winter months and leading up to the winter solstice, far before any of the myths associated with Christians. The Old Testament even mentions pagan customs of cutting down trees and decorating them in Jeremiah 10:2-4 and condemns the practice.
One of the dumbest, most laughable myths that some Christians use to try to explain why they use a Christmas tree is that of Saint Boniface, who was a Christian missionary to the Germans in the Eight Century AD, making him quite a late-comer to this game! Of course, 99% or Christians have probably never even heard this before, and it is certainly not any kind of official teaching. You might ask yourself if you've ever heard of this story, if you are a Christian, before proceeding further. Anyway, the myth is that Saint Boniface found some pagans making a sacrifice to an oak tree and so he ran over and cut it down (with his chainsaw, apparently), and an evergreen popped up in its place, with the green representing resurrection, and the triangular shape representing the Trinity.
Of course this "explanation" doesn't pass the sniff test on any level whatsoever. Not only does the story sound like utter nonsense, but it doesn't explain why Christians would kill an evergreen tree and take it into their houses or why they would decorate it or why they would do it at this time of year. If the evergreen represents resurrection then presumably they would have these trees at EASTER, not Christmas, and they would probably not be killing these trees as a symbol of eternal life.
On the other hand, many pagans had traditions, such as Yuletide, which involving taking an evergreen into one's house far before the Eight Century. It's mentioned in the Eddas in the Fourth century. In particular, they decorated it with things like bells so that they could hear the movements of the spirit that might inhabit the tree. They brought the tree indoors because it was the winter months and they wanted to give the spirit who resided in the tree a warm home. A large Yule Log was burned to symbolically represent the rekindling of the Sun's warmth. The Boniface myth can't quite explain that one either.
If Saint Boniface "invented" the Christmas tree then not only did he do it far after the Pagans were already doing it, but apparently his "invention" was forgotten for almost another thousand years, because decorated trees didn't start becoming popular again in Germany again until about the 1600's. It didn't catch on in the rest of the Christian world until the 1800's when the German tradition was imported to Victorian England. That seems pretty strange if Boniface worked such a memorable "miracle".
Of course, to hear Christians today, you would think that tree decorating was commanded by Jesus in the Sermon on the Mount. They believe that they own and invented this end-of-year festive season, and many balk at the notion that they would have to SHARE this holiday time (aka the Yule-tide) with any other group of people.
They also seem to think that they invented gift-giving. It just goes to show how much at odds Christian beliefs are with reality at this time of year.