menu = {
......

 }

 current_layer = menu

 layers = []

 while True:

     for k in current_layer:

         print(k)

     choice = input('>:').strip()

     if not choice:continue

     if choice in current_layer:

         layers.append(current_layer)

         current_layer = current_layer[choice]

     elif choice == 'q':

         break

     elif choice == 'b':

         if len(layers) != 0:

             current_layer = layers.pop()

         else:

             print('-------Top!-------')