Collapsible Tree Demo
        
          The Collapsible Tree demo shows interactive collapsing and expanding of subtrees of a
          graph. Using the dedicated helper classes for filtering-out parts of a graph and the tree
          layout algorithm, implementing such an interactive application is easy.
        
        
          The main classes used in this demo are FilteredGraphWrapper and
          TreeLayout.
        
        Things to Try
        
          - 
            Click a node with a +/- button to expand or collapse its subtree. Note that there are
            also leaf nodes which cannot be expanded further.
          
 
          - 
            Select an automatic layout style from the drop down in the toolbar. Choosing a new
            style, or expanding and collapsing nodes, triggers a refresh of the layout.
          
 
          - 
            Use the zoom and "Fit Content" buttons in the toolbar to focus on local areas or to view
            the complete graph.