This is a proposal for a presentation at the OCaml 2017 workshop. The presentation will cover B-trees as a data-structure (including motivating why variants of B-trees are often the data-structure of choice for filesystems and databases), and the particular variant that is provided by the \texttt{tjr_btree} library available from GitHub. This library uses code generated from an Isabelle/HOL theory, which is also available from GitHub.