this is the Viking tradition: the yulelog, but many other things - a winter festival celebrating "have stores" and being ALIVE when mid-winter passes on it's way OUT of winter
the did NOT celebrate winter as a pagan religion. they had the town gathering festival because it was a good time to do such a thing, and all cities back then did have days they had festivals of (harvest / yield / being alive) celebration.
the Christmas tree is obviously not the nordic winter festival tradition