code: def lookups(self, request, model_admin):
          
          list_tuple = []
          for article in ArticlePage.objects.all():
              if article.get_parent_section():
                  section_tuple = (
                      article.get_parent_section().id,
                      article.get_parent_section().title
                  )
                  if section_tuple not in list_tuple:
                      list_tuple.append(section_tuple)
          return list_tuple
docs: Returns a list of tuples. The first element in each
          tuple is the coded value for the option that will
          appear in the URL query. The second element is the
          human-readable name for the option that will appear
          in the right sidebar.