diff --git a/gtsam/discrete/DecisionTreeFactor.cpp b/gtsam/discrete/DecisionTreeFactor.cpp
index f0472245b..7ba4c9011 100644
--- a/gtsam/discrete/DecisionTreeFactor.cpp
+++ b/gtsam/discrete/DecisionTreeFactor.cpp
@@ -117,14 +117,6 @@ namespace gtsam {
     return DecisionTreeFactor(keys, result);
   }
 
-  /* ************************************************************************ */
-  DecisionTreeFactor DecisionTreeFactor::apply(ADT::UnaryAssignment op) const {
-    // apply operand
-    ADT result = ADT::apply(op);
-    // Make a new factor
-    return DecisionTreeFactor(discreteKeys(), result);
-  }
-
   /* ************************************************************************ */
   DecisionTreeFactor::shared_ptr DecisionTreeFactor::combine(
       size_t nrFrontals, ADT::Binary op) const {