diff --git a/gtsam/discrete/DecisionTreeFactor.cpp b/gtsam/discrete/DecisionTreeFactor.cpp
index ff18268b1..56f1659dc 100644
--- a/gtsam/discrete/DecisionTreeFactor.cpp
+++ b/gtsam/discrete/DecisionTreeFactor.cpp
@@ -101,6 +101,14 @@ 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 {
diff --git a/gtsam/discrete/DecisionTreeFactor.h b/gtsam/discrete/DecisionTreeFactor.h
index e90a2f96f..e92c82b77 100644
--- a/gtsam/discrete/DecisionTreeFactor.h
+++ b/gtsam/discrete/DecisionTreeFactor.h
@@ -147,8 +147,11 @@ namespace gtsam {
     /// @name Advanced Interface
     /// @{
 
-    /// Inherit all the `apply` methods from AlgebraicDecisionTree
-    using ADT::apply;
+    /**
+     * Apply unary operator (*this) "op" f
+     * @param op a unary operator that operates on AlgebraicDecisionTree
+     */
+    DecisionTreeFactor apply(ADT::UnaryAssignment op) const;
 
     /**
      * Apply binary operator (*this) "op" f