private void RemoveHierarchicalElement()
        {
            var hierarchicalElement = Manager.SelectedElement as HierarchicalElementViewModel;

            if (hierarchicalElement?.ParentViewModel != null)
            {
                hierarchicalElement.ParentViewModel.Subitems.Remove(hierarchicalElement);
            }
            else
            {
                HierarchicalElements.Remove(hierarchicalElement);
            }
        }
        private void AddHierarchicalElement()
        {
            var selectedHierarchicalElement = Manager.SelectedElement as HierarchicalElementViewModel;

            if (selectedHierarchicalElement != null)
            {
                var newItem = new HierarchicalElementViewModel(selectedHierarchicalElement)
                {
                    Name = "Child Element"
                };
                selectedHierarchicalElement.Subitems.Add(newItem);
                newItem.Selected = true;
            }
            else
            {
                var newItem = new HierarchicalElementViewModel(null)
                {
                    Name = "Root Element"
                };
                HierarchicalElements.Add(newItem);
                newItem.Selected = true;
            }
        }