docstr: Enter the Tkinter mainloop.  This function must be called if
  this demo is created from a non-interactive program (e.g.
  from a secript); otherwise, the demo will close as soon as
  the script completes.
code: def mainloop(self, *args, **kwargs):
      """
      Enter the Tkinter mainloop.  This function must be called if
      this demo is created from a non-interactive program (e.g.
      from a secript); otherwise, the demo will close as soon as
      the script completes.
      """
      if in_idle():
          return
      self._top.mainloop(*args, **kwargs)
  
imports: from tkinter import IntVar, Menu, Tk
  from nltk.draw.util import BoxWidget, CanvasFrame, CanvasWidget, OvalWidget, ParenWidget, TextWidget
  from nltk.tree import Tree
  from nltk.util import in_idle
label_desc: Use image node_id 6 for calling the TreeView obj's underlying member method code with example usage: obj.mainloop() without return types