There is this movie that I thought started with "the book" something or "the" something and ended with "master," I don't know. It starts with a kid who, I think, is picked on by other kids for like being a geek, and having an weird looking yellow bike. He ends up going to the library, he gets lost, and ends up in a fantasy world. He goes on some kind of journey I think, I don't remember what happens then, but at the end he wakes up in the library and is happy he's back in reality (only a few hours have passed, if any) and he goes home on his bike.
Please help me find out the name of this movie, it was really good and I'm dying to watch it again, thank you.

The Pagemaster (1994)

There is a kids movie called Neverending Story this child also goes in to a library

Was this movie animated? Because I remember watching a movie similar to the one you described but it was animated. And wasn't the never ending story. Although a version that I remember while he was in the fantasy world I'm sure he came across pirates and some frankenstien thing at the end or something. And I also remember that the kid had a tree house. If your story was animated though. Lols

Maybe The Pagemaster of 1994 with Culkin?