import tkinter as tk
from tkinter import ttk
from tkinter import messagebox as mb
import time
root = tk.Tk()
root.geometry("300x300")
pb1 = ttk.Progressbar(root, orient="horizontal", mode="determinate", maximum=100, value=0)
pb1.place(x=50, y=50)
while pb1['value'] < 100:
pb1['value'] += 10
root.update()
time.sleep(0.5)
if pb1['value'] == 100:
mb.showinfo(message='Загрузка данных завершена, нажмите кнопку Start')
pb1.destroy()
# или
# pb1.place_forget()
root.mainloop()