How to add sub menus in appindicators?

I am using this code to try to add submenus in appindicator

#!/usr/bin/env python
import gobject
import gtk
import appindicator

def clean_quit(w):
  print "in quit"
  gtk.main_quit()

    if __name__ == "__main__":
      ind = appindicator.Indicator ("example-simple-client",
                              "indicator-messages",
                              appindicator.CATEGORY_APPLICATION_STATUS)
  ind.set_status (appindicator.STATUS_ACTIVE)
  ind.set_attention_icon ("indicator-messages-new")

  # create a menu
  menu = gtk.Menu()
  listMenu=gtk.Menu()
  listItems=gtk.MenuItem("Show List")
  listItems.set_submenu(listMenu)
  inews = gtk.MenuItem("Import")
  listMenu.append(inews)
  menu.append(listItems)
  listItems.show()
  # create some
  menu_items=gtk.MenuItem("Quit")
  menu.append(menu_items)
  menu_items.connect("activate", clean_quit)
  menu_items.show()
  ind.set_menu(menu)

  gtk.main()

It's not working - what is wrong in this code?