how to set a checkbutton "true" in python

How do I set a checkbutton true on startup, currently it shows as an empty checkbox when i run my programm. I'd like for the checkbutton to start checked instead of unchecked

This is my code for the checkbutton

self.checkbutton = Checkbutton(self.frame1, text="Automatisch", onvalue=1, pady=12, padx=0, command=self.set_automatic_bool).grid(row=1, column=1, columnspan=5,  sticky=NSEW)