What are decision trees?
A decision tree is a graph that allows you to reach an outcome (a decision) by repeatedly evaluating conditions. Once a condition has been evaluated, you follow the corresponding branch to the next node. This node may either be another condition to be evaluated or it may be a leaf containing a decision.
What are Decision Trees used for?
In the same way that humans use their past experiences to influence their future decisions, a decision tree uses training data to make a decision on what the outcome should be. For example, a simple one level tree may ask if a user has liked Facebook pages about cycling to decide whether or not to show them an advert for a new bicycle.