Prevent duplicate insertion points to be shown in tree viewers

Change-Id: I85b1f3fa57042034c78c5bd30abf5607b3f5acc6
diff --git a/plugins/org.eclipse.emf.compare.ide.ui/src/org/eclipse/emf/compare/ide/ui/internal/contentmergeviewer/tree/provider/TreeMergeViewerItemContentProvider.java b/plugins/org.eclipse.emf.compare.ide.ui/src/org/eclipse/emf/compare/ide/ui/internal/contentmergeviewer/tree/provider/TreeMergeViewerItemContentProvider.java
index 523eca5..2ddb4b2 100644
--- a/plugins/org.eclipse.emf.compare.ide.ui/src/org/eclipse/emf/compare/ide/ui/internal/contentmergeviewer/tree/provider/TreeMergeViewerItemContentProvider.java
+++ b/plugins/org.eclipse.emf.compare.ide.ui/src/org/eclipse/emf/compare/ide/ui/internal/contentmergeviewer/tree/provider/TreeMergeViewerItemContentProvider.java
@@ -448,7 +448,7 @@
 	 */
 	private List<Diff> collectDifferences(Comparison comparison, Iterable<Object> objects) {
 		List<Diff> differences = StreamSupport.stream(objects.spliterator(), false)
-				.filter(EObject.class::isInstance).map(EObject.class::cast)
+				.filter(EObject.class::isInstance).map(EObject.class::cast).distinct()
 				.flatMap(eobject -> comparison.getDifferences(eobject).stream()).collect(Collectors.toList());
 		return differences;
 	}