title: Insert child node in nltk tree
body: <p>Assuming that I can read and edit all tree's leaves labels, using the following code:</p>
  
  <pre><code>for leaf in t.treepositions('leaves'):
    t[leaf] = new_value
  </code></pre>
  
  <p>How could I add a new leaf as a child of the actual leaf t[leaf]? Could be a silly question, but I haven't lot of experience with nltk.</p>