Unable to properly initialize a tkinter scrollbar inside a UI

Question

I'm not an expert python programmer. After some time and effort I've built a tkinter UI that properly works. Recently, I've found myself needing to add a scrollbar inside the frame, since I need to place several new buttons inside an already packed UI, and apparently I'm always missing something.

This would be a minimal reproducible example:

class SampleApp(Tk):
    def __init__(self, *args, **kwargs):
        Tk.__init__(self, *args, **kwargs)
        self.geometry('800x800')

        container = Frame(self)
        container.config(bd=1)
        container.pack(side="top", fill="both", expand=True)
        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        # Create an instance of StartPage and show it
        start_page = StartPage(parent=container, controller=self)
        start_page.grid(row=0, column=0, sticky="nsew")


class StartPage(Frame):
    def __init__(self, parent, controller):
        Frame.__init__(self, parent)
        self.controller = controller

        #initialize variables
        path_working_directory = StringVar()

        def add_working_directory():
            value = askdirectory(title='add_working_directory')
            path_working_directory.set(value)

        #working directory
        Button(self, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="Button1",command=add_working_directory).place(x=10, y=58)
        Entry(self, bd="4", textvariable=path_working_directory).place(x=160, y=60)

        Button(self, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="Button2",command=add_working_directory).place(x=10, y=250)
        Entry(self, bd="4", textvariable=path_working_directory).place(x=160, y=250)

        Button(self, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="Button3",command=add_working_directory).place(x=10, y=600)
        Entry(self, bd="4", textvariable=path_working_directory).place(x=160, y=600)

if __name__ == "__main__":
    app = SampleApp()
    app.mainloop()

This is a working tkinter UI. What I need to add is a scrollbar, so that a user can scroll through the interface and easily see all the buttons. The fact that I'm using classes is making hard for me to understand how to properly add a scrollbar.