title: END is not working in insert function of tkinter Listbox
body: <p>When I click on button to populate the data in list it show following:</p>
  
  <pre><code>Exception in Tkinter callback
  Traceback (most recent call last):
    File "C:\Users\Haseeb Bhai\Anaconda3\lib\tkinter\__init__.py", line 1699, in __call__
      return self.func(*args)
  
  File "E:\Python Development\Book-Store\intermediate.py", line 17, in view_command
      front_end.book_list.insert(END, row)
  
  NameError: name 'END' is not defined
  </code></pre>
  
  <p>I'm calling it with this code:</p>
  
  <pre><code>tkinter.Listbox.insert(END, row) 
  </code></pre>
  
  <p>One more thing here is I want to add the new row at the start of the list. I hope passing 0 as the index will override the previous first value so what should be the index arg to insert the row at the start of the list.</p>