title: Name not defined when using Anytree class
body: <p>I am working with Python's anytree package, and I am trying to iterate over the tree:</p>
  
  <pre><code>from anytree import Node, RenderTree, AsciiStyle
  
  f = Node("f")
  b = Node("b", parent=f)
  a = Node("a", parent=b)
  
  print(RenderTree(f, style=AsciiStyle()).by_attr())
  
  
  for node in LevelOrderIter(f):
      print node.name
  </code></pre>
  
  <p>However, for some reason I am getting an error <code>NameError: name 'LevelOrderIter' is not defined</code>. </p>
  
  <p>I have installed anytree (it works creating nodes, etc.) and I seem to be correct according to syntax: <a href="http://anytree.readthedocs.io/en/latest/apidoc/anytree.iterators.html#anytree.iterators.LevelOrderIter" rel="nofollow noreferrer">http://anytree.readthedocs.io/en/latest/apidoc/anytree.iterators.html#anytree.iterators.LevelOrderIter</a></p>
  
  <p>Any ideas what it does not work?</p>
  
  <p>Full error:</p>
  
  <pre><code>f
  +-- b
      +-- a
  Traceback (most recent call last):
    File "aa.py", line 10, in &lt;module&gt;
      for node in LevelOrderIter(f):
  NameError: name 'LevelOrderIter' is not defined
  </code></pre>