Hierarchical Clustering: Explain It To Me Like I'm 10

This is part numero tres of the Explaining Machine Learning Algorithms to a 10-Year Old series. If you read the two previous ones about XGBoost Regression and K-Means Clustering, then you know the drill. We have a scary-sounding algorithm, so let's strip it of its scary bits and understand the simple intuition behind it. In the same vein as K-Means Clustering, today we are going to talk about another popular clustering algorithm -- Hierarchical Clustering. Let's say a clothing store has collected the ages of 9 of its customers, labeled C1-C9, and the amount each of them spent at the store in the last month.