Looking for a kid adventure/fantasy movie, probably European, from the 80s-90s (not later). There was a red-haired boy called Peter, who discovers a magic tree, goes through it to some magic world and meets the vikings (or fighters of some sort). He keeps coming there, and these journeys are kept in secret from his parents. I think only his girlfriend knew about it. Later in the movie a mayor wants to cut the tree, and Peter convinces the vikings to appear in the city so that everyone would know that the tree has magic powers. The vikings come out of the tree in the middle of a city parade or some festivity.