title: Only last value displays in tkinter listbox
body: <p>I iterate through either key or values from my config.ini file and insert it into my listbox, however, only the last value is inserted.</p>
  <p>My config files has two sections [TEST1] and [TEST2]. Only TEST2 shows in the listbox, printing the keys however, prints both TEST1 and TEST2.</p>
  <p>Thank you in advance.</p>
  <pre><code>from tkinter import *
  from configobj import ConfigObj
  
  root = Tk()
  
  parser = ConfigObj(&quot;config1.ini&quot;)
  options = parser.iterkeys()
  
  for k in options:
      print(k)
  
  listbox = Listbox(root, width=50)
  listbox.place(x=145, y=230)
  listbox.insert('end', k)
  
  root.title('Test')
  root.geometry('500x500')
  root.mainloop()
  </code></pre>