This is my idea, I still need to work out the details.
def map1(): for i in range(120):#it will show this map for 120 seconds while True: grass() trees() pygame.display.flip()
I figured out the timer after your hint and I plan to temporarily draw a block to measure the speed and how the background will move when the game is running.
I'm also in the process of drawing the trees and will use a loop to randomly show them on either side as the game screen moves.
I'll work on it this weekend and show my progress Monday.