'Return a box containing the main tree (the one showing
Host/Interfaces/Services) as its content.'

@scrollable(width=250)
def create_main_tree_view(self, model):

    view = Gtk.TreeView(model)
    view.set_activate_on_single_click(True)
    view.set_search_column((-1))
    view.set_enable_tree_lines(True)
    view.expand_all()
    renderer = Gtk.CellRendererText()
    column = Gtk.TreeViewColumn('Host/Interfaces/Services', renderer, text=12)
    view.append_column(column)
    view.set_expander_column(column)
    selection = view.get_selection()
    selection.connect('changed', self.on_main_tree_selection)
    return view
