This is one of the lesser-known Christmas myths, but to be honest, it would be pretty cool if true. The story goes that Sami shamans in Scandinavia would dress in red and white to match the colors of the psychedelic Amanita mushrooms they peddled. In the winter, they couldn’t make their door-to-door sales due to snowstorms blocking many doors, so they would climb in through the chimney. The mushrooms would then be hung to dry, for example on branches of a tree brought inside for that purpose.
Unfortunately, the details don’t check out. Houses and yurts of the area were not built in ways that would block the occupants in all winter; there’s no documentation of mushrooms being distributed this way or dried on indoor trees when they could just be hung in more convenient ways; and Santa’s red outfit came from a different European tradition entirely.
But it is true that there is a Scandinavian tradition (among the Sami people, in particular) of using those red-and-white mushrooms for religious visions and as medicine. In one tradition, the shaman might climb up an indoor tree to the smoke hole (or chimney) to look out. So while parts of the story may sound familiar, inviting a shaman over to trip on mushrooms is an entirely separate celebration from the gift-giving Christmas ritual.