1. A method comprising, by one or more computing devices: evaluating a decision tree in interpreted mode; modifying the decision tree by annotating each decision in the decision tree with instructions determined based on statistics collected during evaluation of the decision tree; generating an executable version of the decision tree, the executable version comprising executable code optimized based on the instructions; executing the executable code; and verifying the executable code by comparing a result of executing the executable code with a result of evaluating the decision tree in interpreted mode.