Trees – A Primer by Jeremy Kun.
From the post:
This post comes in preparation for a post on decision trees (a specific type of tree used for classification in machine learning). While most mathematicians and programmers are familiar with trees, we have yet to discuss them on this blog. For completeness, we’ll give a brief overview of the terminology and constructions associated with trees, and describe a few common algorithms on trees. We will assume the reader has read our first primer on graph theory, which is a light assumption. Furthermore, we will use the terms node and vertex interchangeably, as mathematicians use the latter and computer scientists the former.
A nice introduction/refresher on tree data structures.