title: Height of a tree with only one node
body: <p>According to Wikipedia, </p>
  
  <blockquote>
    <p>The height of a tree is the length of the path from the root to the
    deepest node in the tree. A (rooted) tree with only one node (the
    root) has a height of zero (or one).</p>
  </blockquote>
  
  <p>I dont get it - is it zero or one (or both)?</p>