> #--- snip here ---#
> require 'fox'
> include Fox
> class MainWindow < FXMainWindow
>   def draw_display
>     @tree = FXTreeList.new(@group1, 0, nil, 0,
>         (FRAME_SUNKEN|FRAME_THICK|LAYOUT_FILL_X|LAYOUT_FILL_Y|
>          LAYOUT_TOP|LAYOUT_RIGHT|TREELIST_SHOWS_LINES|
>          TREELIST_SHOWS_BOXES|TREELIST_ROOT_BOXES|
>          TREELIST_EXTENDEDSELECT))

      @tree.create

>     @one = @tree.addItemLast(nil, "One", nil, nil)
>     @two = @tree.addItemLast(nil, "Two", nil, nil)
>     @three = @tree.addItemLast(nil, "Three", nil, nil)
>     1.upto(30) {|x|
>         @tree.addItemLast(@one, "Item 1-#{x}", nil, nil)
>     }
>   end

Try that.  Fox widgets need to be explicitly 'created' when they are added after the
application.create call.  And beware calling your 'draw_display' from initialize now.  The widget
will be created in the first pass, then throw an error in the second pass (when it tries to create
it again).