Jesus was not born Dec. 25th. In fact, nobody knows for sure when Jesus was born. The best, educated guess as to when Jesus was born is the beginning of September.
(https://reasonsforhopejesus.com/jesus-born-september/)
Christianity was not an established religion until after Jesus' death.
(Some people did worship Jesus before the crucifixion, but, Christianity was not a well established religion with established traditions until after Jesus' death.)
Back then, there were a lot of Pagans. So, in order to attract them to convert to Christianity, they had to make Christianity as similar to Paganism as possible. Pagans have a holiday tradition they celebrate December 20-23 called Yule, which involves decorating pine trees, bringing other ever green plants, including Mistletoe, Pine Trees and Yew, into the house. The Pagan, Yule celebration also included exchanging gifts and some other things that Christians do now.
(https://en.m.wikipedia.org/wiki/Wheel_of_the_Year)
Christians did some of the same things on the date that was chosen to celebrate Jesus' birth.
The plan worked. A lot of Pagans changed their religion to Christianity.
To this day, Christians still do a lot of things that were borrowed from Paganism, judaism and several other religions. Most Christians have no idea that things like decorating a Pine Tree or Dec. 25, originally had nothing to do with Jesus at all.
