Tkinter button not working geometry error

I'm learning tkinter and trying to make a button but when I run my code an error comes up saying

.TclError: cannot use geometry manager grid inside . which already has slaves managed by pack

This is my code:

import tkinter
from tkinter import Button
window=tkinter.Tk()
#title
window.title("Elvoria")
#text
label=tkinter.Label(window, text = "Welcome To Elovria").pack()
#button
bt = Button(window,text="Start")
bt.grid(column=1,row=1)
window.mainloop()