<DataTemplate>

                         <TextBlock Text="{Binding Data.ChapterName}" />

                    </DataTemplate>

                    </ig:NodeLayout.ItemTemplate>

                </ig:NodeLayout>

            </ig:XamDataTree.GlobalNodeLayouts>

        </ig:XamDataTree>

code behind:

 private void XamContextMenu_Opening(object sender, OpeningEventArgs e)

   {

       //this gives error 

       List<XamDataTreeNode> elements = e.GetClickedElements<XamDataTreeNode>();

   }

Note: This works fine with the XamTree 
(List<XamTreeItem> elements = e.GetClickedElements<XamTreeItem>();)

Thanks in advance.