Have You Heard About Unsupervised Decision Trees

Summary: Unless you're involved in anomaly detection you may never have heard of Unsupervised Decision Trees. It's a very interesting approach to decision trees that on the surface doesn't sound possible but in practice is the backbone of modern intrusion detection. I was at a presentation recently that focused on stream processing but the use case presented was about anomaly detection. When they started talking about unsupervised decision trees my antenna went up. What do you mean unsupervised decision trees?