private void ShowContainment([NotNull] IModelRelationship addedRelationship)
        {
            var diagram = DiagramService.LatestDiagram;

            if (diagram.NodeExists(addedRelationship.Source) && diagram.NodeExists(addedRelationship.Target))
            {
                DiagramService.UpdateParent(addedRelationship.Target, addedRelationship.Source);
            }
        }