how to make objects bounce in trutle

import turtle
from time import sleep

# Screen setup
wn = turtle.Screen()
wn.setup(width = 500, height = 500)
wn.tracer(0)

# Object setup (The ball)
ball = turtle.Turtle()
ball.color("black")
ball.shape("circle")
wn.update()

running = True

# you can change the shapes by changing the value of x and y
x = 5
y = 2

def bounce():
    global x,y
    ball.setx(ball.xcor() + x)
    ball.sety(ball.ycor() + y)
    if ball.ycor() > 250:
        ball.sety(250)
        y = y * (-1)
    elif ball.ycor() < -256:
        ball.sety(-256)
        y = y * (-1)
    elif ball.xcor() > 250:
        ball.setx(250)
        x = x * (-1)
    elif ball.xcor() < -256:
        ball.setx(-256)
        x = x * (-1)
def end():
    global running
    running = False
def stop():
    global end
    wn.onkeypress(end,"Escape")
    wn.listen()

# * if you want to let the ball stop drawing press escape 
while running == True:
    stop()
    bounce()
    sleep(0.002)
    wn.update()