def insertLeft(root, newBranch):
  """Insert a new left node."""
  t = root.pop(1) # get the left child
  if len(t) > 1:
    # add new left child to root and 
    # make old left child it's left child.
    root.insert(1, [newBranch, t, []])
  else:
    root.insert(1, [newBranch, [], []])
  return root