What is the name of a book about a boy named Jericho (or Jethro not sure)? Who turns into a tree?

I can't remember what it is called. I just remember I read it in like 4th or 5th grade. The boy falls in love with a girl but he turns into a tree at night or something like that. I can't remember and it is really bothering me. PLEASE HELP!!

What is the name of a book about a boy named Jericho (or Jethro not sure)? Who turns into a tree?
it's called "the wish giver" by bill brittain