Something

        self.lstFiles.grid(row=1, column=0, columnspan=2)
        buttonFrame = tk.Frame(self)
        buttonFrame.grid(row=2, column=2, sticky='ew')
        self.btnAdd = tk.Button(buttonFrame, text="Add...", command=self.addFiles)
        self.btnAdd.grid(row=0, column=0, sticky='ew')
        self.btnRemove = tk.Button(buttonFrame, text="Remove",
                                   command=self.removeFiles)
        self.btnRemove.grid(row=0, column=1, sticky='ew')