Decision Trees -- OpenCV 2.4.13.4 documentation

To reach a leaf node and to obtain a response for the input feature vector, the prediction procedure starts with the root node. From each non-leaf node the procedure goes to the left (selects the left child node as the next observed node) or to the right based on the value of a certain variable whose index is stored in the observed node. So, in each node, a pair of entities (variable_index, decision_rule (threshold/subset)) is used. This pair is called a split (split on the variable variable_index). Once a leaf node is reached, the value assigned to this node is used as the output of the prediction procedure.