new_contents: """Output a tree of stars like so:
  
      *
     ***
      *
     ***
    *****
      *
     ***
    *****
   *******
  
  Input argument is the number of levels to the tree (3 in this example)
  """
  from sys import argv
  
  
  def main(levels):
      for level in xrange(levels):
          for sub_level in xrange(level+2):
              spaces = (levels+2-sub_level) * ' '
              stars = ((2 * sub_level) + 1) * '*'
              print '{spaces}{stars}'.format(spaces=spaces, stars=stars)
  
  
  if __name__ == '__main__':
      main(int(argv[1]))
  
subject: Add solution to tree_stars.py