Four tree flat wings. (5 ltr. paint tin for scale) Photo taken in the workshop. The left hand flat in this photograph goes audience left and the others - audience right. I have forced the perspective a little with these trees, making the trunks of the upstage one thinner than the front one. You can't do this trick too robustly otherwise a character arriving behind the upstage wing appears a giant compared to his compatriot arriving further downstage.

Note I have kept the "mountains" running behind each flat. Which in reality wouldn't work as the actors would be walking between mountains to enter the stage. Strangley the audience doesn't query this - but then in musicals they don't query why people suddenly burst into song either!