Decision trees. A decision tree is a special type of tree where the root and each interior node correspond to a variable; an arc to a child represents a possible value of that variable. A leaf represents the predicted value of target variable given the values of the variables represented by the path from the root. Following a route from the root node to a leaf node at each interior node we have to decide, which path to follow. Effectively each possible path encodes a decision rule. A Example for a decision tree. By following from the root node (top) to a leaf node (bottom) one has to make a decision at every interior node. B Corresponding set of decision rules.