This is my recommended book on multilevel models, and it's also much more than that. Even if you have no interest whatsoever in multilevel models, the first part of this book has very useful things to say about designing and interpreting experiments for causal inference, a topic which is sorely neglected in many modeling and machine learning books.
One caveat is that all the MCMC examples in this book use Bugs, which was Windows-only and is now somewhat obsolete. You should not actually use Bugs, but rather JAGS instead, which is mostly syntax-compatible.