John 1:17, “For the law was given through Moses; grace and truth came through Jesus Christ.”
It is true that some Christian symbols are or were used in paganism, but this is certainly not the association a practising Christian has got to have with the symbol, and it is certainly not the only meaning that can be applied to a symbol.
So no, your Christmas Tree is not evil. Nor are the other symbols of Christmas: bells, balls, angels etc.