What is the name of this book?

I read a book a long time ago about this guy whose mother has died, but before dying she made a kind of snowglobe (it might not be a snowglobe, might be a carving inside glass, don't remember exactly) representing their house (or an old tree near their house, something like that). He picks up the snowglobe and it takes him to a parallel universe where his mother is alive and he was born as a girl (whom he meets) and so on. Not very important but just annoying not to remember. Thanks for any help.