Well,according to research, in the Roman pagan festivals for the early Christians to avoid precautions they would deck their homes with Saturnalia holly or otherwise known as a mistletoe. The early church did not actually celebrate the birth of Christ in December until Telesphorus, who was the second Bishop of Rome had declared that Church services shall be held during the time of Christ being born to celebrate. However, no one was quite sure when Christ was born do it was often held in September, which was when the Jewish Feast Of Trumpets was happening.
Constantine the Great, was the first Christian Roman Emperor to introduced Christmas as an immoveable feast on the 25th