I’ve dealt with this before, among other places here. As many times as you’ve heard it said that Christians just “took over” the Roman Saturnalia celebration and turned it into Christmas, that “fact” actually rests on fairly shaky ground.
There’s good reason to believe that the date was chosen for symbolic and theological reasons, not simply as a substitutionary placeholder for Roman orgies.
To be clear, the argument here is not that Jesus was in fact born on December 25. The argument is that the early church had other reasons for choosing the date than just usurping a heathen festival.
Which means that that guy in your church who says you’re going to hell because you have a Christmas tree is putting his confidence in questionable scholarship.