custom_adminsite_menu.py

import my_app

@register.assignment_tag(takes_context=True)
def get_menu(context, request):
    """
    :type request: WSGIRequest
    """
    if not isinstance(request, WSGIRequest):
        return None

    # Try to get app list
    template_response = admin.site.index(request)
    template_response_my_admin = my_app.admin.my_adminsite_instance.index(request)
    try:
        app_list = template_response.context_data['app_list'] + template_response_my_admin.context_data['app_list']
    except Exception:
        return

    return Menu(context, request, app_list).get_app_list()