如何用类方法封装Tkinter界面并实现功能串联？

import tkinter as tk
import time

class WindowManager:
    def __init__(self):
        self.root = tk.Tk()
        self.root.title("Progress Bar Example")
        self.root.geometry("300x200")
        self.root.state('iconic') #最小化窗口

        self.progress_var = tk.DoubleVar()
        self.progress_bar = None


    def create_progress_bar(self):
        self.progress_bar = tk.ttk.Progressbar(self.root, variable=self.progress_var, maximum=100)
        self.progress_bar.pack(pady=20)

    def button_start(self, command):
        start_button = tk.Button(self.root, text="Start", command=command)
        start_button.pack()

    def button_quit(self):
        quit_button = tk.Button(self.root, text="Quit", command=self.root.quit)
        quit_button.pack()

    def update_progress(self):
        for i in range(101):
            self.progress_var.set(i)
            self.root.update()
            time.sleep(0.1)


if __name__ == "__main__":
    ob = WindowManager()
    ob.create_progress_bar()

    def start():
        ob.update_progress()
        ob.button_quit()

    ob.button_start(start)
    ob.root.mainloop()