code: public void initalizeTreeState()
      {
          _lastNodeExpandedImage = IMAGE_NODE_EXPAND_LAST;
          _nodeExpandedImage = IMAGE_NODE_EXPAND;
          _lastNodeCollapsedImage = IMAGE_NODE_COLLAPSE_LAST;
          _nodeCollapsedImage = IMAGE_NODE_COLLAPSE;
          _lastLineJoinImage = IMAGE_LINE_JOIN_LAST;
          _lineJoinImage = IMAGE_LINE_JOIN;
          _verticalLineImage = IMAGE_LINE_VERTICAL;
          _imageSpacer = IMAGE_SPACER;
          _defaultIcon = DEFAULT_ICON;
          _imageRoot = null;
  
          _selectionAction = null;
          _expansionAction = null;
      }
docs: This method initalizes the state of the properties to their default values used by the
  tree tag to create the tree markup.