TEXT_EDIT_MENU.py

import bpy

class SubMenu(bpy.types.Menu):
    bl_idname = "OBJECT_MT_select_submenu"
    bl_label = "Select"

    def draw(self, context):
        layout = self.layout

        layout.operator("object.select_all", text="Select/Deselect All")

        # access this operator as a submenu
        layout.operator_menu_enum("object.select_by_type", "type", text="Select All by Type...")




def menu_draw(self, context):
    self.layout.menu("OBJECT_MT_select_submenu")

bpy.utils.register_class(SubMenu)
bpy.types.TEXT_MT_templates.append(menu_draw)