diff --git a/OMDSServiceDefinition/src/main/java/at/vvo/omds/client/gui/TreeHelper.java b/OMDSServiceDefinition/src/main/java/at/vvo/omds/client/gui/TreeHelper.java
index a90ab6ed..f95a98fd 100644
--- a/OMDSServiceDefinition/src/main/java/at/vvo/omds/client/gui/TreeHelper.java
+++ b/OMDSServiceDefinition/src/main/java/at/vvo/omds/client/gui/TreeHelper.java
@@ -166,20 +166,23 @@ public class TreeHelper {
     public TreeItem<Object> addAprioriToCalc(TreeItem<Object> calcItem, TreeItem<Object> aprioriItem)
             throws InvocationTargetException, NoSuchMethodException, InstantiationException, IllegalAccessException {
         for (TreeItem<Object> aprioriChild : aprioriItem.getChildren()) {
-
-            List<TreeItem<Object>> matchingChildren = calcItem.getChildren().stream()
-                    .filter(c -> ((ProduktbausteinType) c.getValue()).getId()
-                            .equals(((ProduktbausteinType) aprioriChild.getValue()).getId()))
-                    .toList();
-
-            if (matchingChildren.isEmpty()) {
-                TreeItem<Object> newChild = cloneTreeItem(aprioriChild);
-
-                calcItem.getChildren().add(newChild);
-                addAprioriToCalc(newChild, aprioriChild);
-            } else {
-                for (TreeItem<Object> matchingChild : matchingChildren) {
-                    addAprioriToCalc(matchingChild, aprioriChild);
+            boolean isInCalc = false;
+            int i = 0;
+            for (TreeItem<Object> calcChild : calcItem.getChildren()) {
+                if (((ProduktbausteinType) calcChild.getValue()).getId().equals(((ProduktbausteinType) aprioriChild.getValue()).getId()) || isNotIncluded.contains(calcChild)) {
+                    isInCalc = true;
+                    if (!aprioriChild.getChildren().isEmpty()) {
+                        calcChild = addAprioriToCalc(calcChild, aprioriChild);
+                        calcItem.getChildren().set(i, calcChild);
+                    }
+                }
+                i++;
+            }
+            if (!isInCalc) {
+                TreeItem<Object> missingCalcItem = cloneTreeItem(aprioriChild);
+                calcItem.getChildren().add(missingCalcItem);
+                if (!isNotIncluded.contains(missingCalcItem)) {
+                    isNotIncluded.add(missingCalcItem);
                 }
             }
         }