Santa is a contraction of St Nicholas, the Turkish Saint.
Flying reindeer are a common hallucination when taking fly agaric mushrooms, although they can kill you. That's why shamen would drink reindeer urine instead, as hallucinogenic and non fatal.
There is only one entrance to such shamanic buildings so the door is also the chimney.
The Holly King flies through the air on reindeer in an obvious state of intoxication. His colours are even the same as the fly agaric.
The two traditions have become conflated,but not in this house, we have no truck with Santa here, only Father Christmas, the Holly King.