请问一下_tkinter.TclError: unknown option "-label"

#-*- encoding=UTF-8 -*-
from tkinter import *
'''from tkinter.messagebox import *'''
import tkinter as tk
from random import *
root=Tk()
menubar=Menu(root)
def drawings():
import 五环
def easy():
count1=0
for i in range(10):
x=randint(0,10)
y=randint(0,10)
print(x,'+',y,'=')
answer=int(input("your answer is:"))
if x+y==answer:
count1=count1+1
print("您的得分为:",count1)
if count1>=8:
print("恭喜您闯关成功，请进入下一关!")
else:
print("很遗憾未成功，请重试！")
def medium():
count2=0
for i in range(10):
x=randint(0,100)
y=randint(0,100)
print(x,'+',y,'=')
answer=int(input("your answer is:"))
if x+y==answer:
count2=count2+1
print("您的得分为:",count2)
if count2>=8:
print("恭喜您闯关成功，请进入下一关!")
else:
print("很遗憾未成功，请重试！")
def hard():
count3=0
for i in range(10):
x=randint(0,1000)
y=randint(0,1000)
print(x,'+',y,'=')
answer=int(input("your answer is:"))
if x+y==answer:
count3=count3+1
print("您的得分为:",count3)
if count3>=8:
print("恭喜您闯关成功，请进入下一关!")
else:
print("很遗憾未成功，请重试！")
mathmenu=Menu(menubar,tearoff=0)
mathmenu.add_command=Menu(label='简单题目',command=easy)
mathmenu.add_command=Menu(label='中等题目',command=medium)
mathmenu.add_command=Menu(label="困难题目",command=hard)
menubar.add_cascade(label="数学游戏",menu=mathmenu)
drawmenu=Menu(menubar,tearoff=0)
drawmenu.add_command(label="画五环",command=drawings)
drawmenu.add_command(label="Matplotlib画四叶草")
menubar.add_cascade(label="画画游戏",menu=drawmenu)
helpmenu=Menu(menubar,tearoff=0)
helpmenu.add_command(label="关于")
helpmenu.add_separator()
helpmenu.add_command(label="关闭",command=root.destroy)
menubar.add_cascade(label="帮助",menu=helpmenu)
root.config(menu=menubar)
root.mainloop()
结果报错：_tkinter.TclError: unknown option "-label"。请问大神们这是为什么呀？
结果报错