Trees are one of those data structures that feel simple at first — and then show up everywhere once you start building real systems or doing interviews. File systems. Org charts. DOM trees. Segment trees. Tries. You name it. This post breaks down what trees are, how they work, and the core vocabulary and traversal algorithms you need for interviews.
What is a tree?
A tree is a hierarchical data structure that organizes data in a parent → child relationship. The easiest mental model is an upside-down family tree: