[Python] I cannot launch a TopLevel window after FileDialog execution

Why can I not show a TopLevel window after launching the FileDialog module?

I would like to show a window with a waiting message after executing FileDialog code.

• 
  If I create the TopLevel window before calling FileDialog, the window is displayed and then the FileDialog code is executed.
  
  
• 
  But if I run FileDialog first, then create the TopLevel, this window is not displayed.
  

This code works fine:

import time
from tkinter import filedialog
from tkinter import *

root = Tk()
root.title("Main window")
root.geometry("400x200")
topLevelWindow = Toplevel(root)
topLevelWindow.title("Secondary window")
topLevelWindow.geometry("400x200")
Label(topLevelWindow, text="Plaese wait...").pack()

# Choose a file and save the path
filename = filedialog.askopenfilename(initialdir = "/",title = "Select file",filetypes = [("All files", "*.*")])
print("File path: ", filename)


But if I execute TopLevel code after FileDialog, it does not show the TopLevel window:

import time
from tkinter import filedialog
from tkinter import *

root = Tk()
root.title("Main window")
root.geometry("400x200")

# Choose a file and save the path
filename = filedialog.askopenfilename(initialdir = "/",title = "Select file",filetypes = [("All files", "*.*")])

topLevelWindow = Toplevel(root)
topLevelWindow.title("Secondary window")
topLevelWindow.geometry("400x200")
Label(topLevelWindow, text="Plaese wait...").pack()

print("File path: ", filename)


Thanks in advance for any help!

I wish to launch TopLevel windows after the FileDialog execution.

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