The Bible itself describes tree decoration as a pagan tradition.

Jeremiah 10:2-5:

2 Thus saith the Lord, Learn not the way of the heathen, and be not dismayed at the signs of heaven; for the heathen are dismayed at them.

3 For the customs of the people are vain: for one cutteth a tree out of the forest, the work of the hands of the workman, with the axe.

4 They deck it with silver and with gold; they fasten it with nails and with hammers, that it move not.

5 They are upright as the palm tree, but speak not: they must needs be borne, because they cannot go. Be not afraid of them; for they cannot do evil, neither also is it in them to do good.