If you're interested in B+Trees, and especially if you find yourself implementing one, go read this: https://w6113.github.io/files/papers/btreesurvey-graefe.pdf

I certainly haven't read the entire thing but gosh there's some good bits. E.g. "B-trees Versus Hash Indexes" - tons of insights jampacked together into a couple pages for anyone who hasn't already been exposed to B-trees in detail (e.g. in a research context vs the usual data structures class)