How to use the imgui.begin function in imgui

if imgui.begin_main_menu_bar():
            if imgui.begin_menu("File", True):

                clicked_quit, selected_quit = imgui.menu_item(
                    "Quit", 'Cmd+Q', False, True
                )

                if clicked_quit:
                    exit(1)

                imgui.end_menu()
            imgui.end_main_menu_bar()

        imgui.show_test_window()

        imgui.begin("Custom window", True)
        imgui.text("Bar")
        imgui.text_colored("Eggs", 0.2, 1., 0.)
        imgui.end()

        gl.glClearColor(1., 1., 1., 1)
        gl.glClear(gl.GL_COLOR_BUFFER_BIT)

        imgui.render()
        impl.render(imgui.get_draw_data())
        glfw.swap_buffers(window)

    impl.shutdown()
    glfw.terminate()

if imgui.begin_main_menu_bar():
            if imgui.begin_menu("File", True):

                clicked_quit, selected_quit = imgui.menu_item(
                    "Quit", 'Cmd+Q', False, True
                )

                if clicked_quit:
                    exit(1)

                imgui.end_menu()
            imgui.end_main_menu_bar()

        imgui.show_test_window()

        imgui.begin("Custom window", True)
        imgui.text("Bar")
        imgui.text_colored("Eggs", 0.2, 1., 0.)
        imgui.end()

        gl.glClearColor(1., 1., 1., 1)
        gl.glClear(gl.GL_COLOR_BUFFER_BIT)

        imgui.render()

        SDL_GL_SwapWindow(window)

    renderer.shutdown()
    SDL_GL_DeleteContext(gl_context)
    SDL_DestroyWindow(window)
    SDL_Quit()

on_exit()
                try:
                    sys.exit()
                except SystemExit as e:
                    time.sleep(0.5)
                    # sys.exit()
                    # sys.terminate()
                    os._exit(1)

            pygame_renderer.process_event(event)

        imgui.new_frame()
        if params.provide_default_window:
            imgui.set_next_window_position(0, 0)
            imgui.set_next_window_size(win_size[0], win_size[1])
            imgui.begin("Default window")
        gui_loop_function()
        if params.provide_default_window:
            imgui.end()
        ImGuiImageLister._heartbeat()

        # note: cannot use screen.fill((1, 1, 1)) because pygame's screen
        #       does not support fill() on OpenGL surfaces
        gl.glClearColor(1, 1, 1, 1)
        gl.glClear(gl.GL_COLOR_BUFFER_BIT)
        imgui.render()
        pygame_renderer.render(imgui.get_draw_data())
        pygame.display.flip()

        imgui_cv._clear_all_cv_textures()
        imgui_ext.__clear_all_unique_labels()

def on_frame():
    if imgui.begin_main_menu_bar():
        if imgui.begin_menu("File", True):
            clicked_quit, selected_quit = imgui.menu_item(
                "Quit", 'Cmd+Q', False, True
            )
            if clicked_quit:
                exit(1)
            imgui.end_menu()
        imgui.end_main_menu_bar()
    imgui.show_test_window()
    imgui.begin("Custom window", True)
    imgui.text("Bar")
    imgui.text_colored("Eggs", 0.2, 1., 0.)
    imgui.end()

if imgui.begin_main_menu_bar():
            if imgui.begin_menu("File", True):

                clicked_quit, selected_quit = imgui.menu_item(
                    "Quit", 'Cmd+Q', False, True
                )

                if clicked_quit:
                    exit(1)

                imgui.end_menu()
            imgui.end_main_menu_bar()

        imgui.show_test_window()

        imgui.begin("Custom window", True)
        imgui.text("Bar")
        imgui.text_colored("Eggs", 0.2, 1., 0.)
        imgui.end()

        imgui.render()
        self.imgui.render(imgui.get_draw_data())

def main():
    global ERROR
    renderer = NXRenderer()
    currentDir = os.getcwd()

    while True:
        renderer.handleinputs()

        imgui.new_frame()

        width, height = renderer.io.display_size
        imgui.set_next_window_size(width, height)
        imgui.set_next_window_position(0, 0)
        imgui.begin("", 
            flags=imgui.WINDOW_NO_TITLE_BAR | imgui.WINDOW_NO_RESIZE | imgui.WINDOW_NO_MOVE | imgui.WINDOW_NO_SAVED_SETTINGS
        )
        imgui.begin_group()

        imgui.text("Welcome to PyNX!")
        imgui.text("Touch is supported")
        imgui.text("Current dir: " + os.getcwd())

        if os.getcwd() != "sdmc:/":
            imgui.push_style_color(imgui.COLOR_BUTTON, *FOLDER_COLOR)
            if imgui.button("../", width=200, height=60):
                os.chdir("..")
            imgui.pop_style_color(1)
        
        dirs = []
        files = []

def _heartbeat(self):
        if not self.opened:
            return
        if self.current_image == "":
            self._select_first_image()
        imgui.set_next_window_position(self.position.x, self.position.y, imgui.APPEARING)
        imgui.set_next_window_size(self.actual_window_startup_size().x, self.actual_window_startup_size().y,
                                   imgui.APPEARING)
        expanded, self.opened = imgui.begin("Imgui Image Lister")
        self._show_list()
        imgui.same_line()
        self._show_image()
        imgui.end()