unable to properly initialize a tkinter Scrollbar

Question

I've been trying to instantiate a tkinter scrollbar inside an already working UI. However, all my attempts failed and I'm unable to tell what I'm doing wrong.

I've been trying to add a scrollbar inside the frame "second_frame", inside the StartPage class, which is the one I'm using to show my widgets:

class SampleApp(Tk):
    global cnfg #global variable for config (data caching management)

    def __init__(self, *args, **kwargs):

        Tk.__init__(self, *args, **kwargs)
        self.geometry('800x800')

        # Gianluca: init config
        # self.init_config_parser()

        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")
        start_page.pack(fill=BOTH, expand=1)


class StartPage(Frame):

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

        #initialize variables
        path_working_directory = StringVar()

        my_canvas = Canvas(parent)
        my_canvas.pack(side=LEFT, fill=BOTH, expand=1)

        my_scrollbar = ttk.Scrollbar(parent, orient=VERTICAL, command=my_canvas.yview)
        my_scrollbar.pack(side=RIGHT, fill=Y)

        my_canvas.configure(yscrollcommand=my_scrollbar.set)
        my_canvas.bind('<Configure>', lambda e: my_canvas.configure(scrollregion = my_canvas.bbox("all")))

        second_frame = Frame(my_canvas)
        my_canvas.create_window((0,0), window=second_frame, anchor='nw')

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

        #title
        label_title = Label(self, text="Genkidama Migrations", bg="#8F8FBC", fg="white", relief="groove", width=20, font=("Adobe Garamond Pro", 20, "italic"))
        label_version = Label(self, text="Version 1.0", bg="#F0F0FF", font=("times new roman", 8, "bold"))
        label_title.pack(side="top", fill="x", pady=10)
        label_version.place(relx=1.0, rely=0.0, anchor="ne")

        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="1",command=add_working_directory).place(x=10, y=58)
        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="2",command=add_working_directory).place(x=10, y=158)
        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="31",command=add_working_directory).place(x=10, y=258)
        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="41",command=add_working_directory).place(x=10, y=358)
        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="51",command=add_working_directory).place(x=10, y=458)
        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="61",command=add_working_directory).place(x=10, y=558)
        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="71",command=add_working_directory).place(x=10, y=658)
        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="81",command=add_working_directory).place(x=10, y=758)
        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="91",command=add_working_directory).place(x=10, y=858)
        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="001",command=add_working_directory).place(x=10, y=958)
        Button(second_frame, overrelief="ridge", bg="#E0E0EE", activebackground="floral white", text="0001",command=add_working_directory).place(x=10, y=1000)

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

However, even if the code works, I cant' really see the scrollbar nor the buttonsimage of my current UI. What am I doing wrong?