The Xmas tree probably originates from the Nordic" Tree of life ". I remember reading it was used to celebrate life and the return of light during the dark cold winters in the north

To celebrate and remember the return of the sun, lights were used to chase away the dark; green as a symbol of returning life, like vegetation and plants, and red probably symbolises fruit and harvest.

There are several versions and interpretation, so it probably depends in which country it was used and in which century.

Santa Claus , originally Saint Nicolaus, was merged with Wodan (Nordic God). Many old Germanic/Nordic religions were integrated with Christian symbolism and rituals.

check this link for more general info.