title: Big O(h) vs. Big O(logn) in trees
body: <p>I have a question on time complex in trees operations.
  <br>It's said that (Data Structures, Horowitz et al) time complexity for insertion, deletion, search, finding mins-maxs, successor and predecessor nodes in BSTs is of <code>O(h)</code> while those of AVLs makes <code>O(logn)</code>. 
  <br>I don't exactly understand what the difference is. With <code>h=[logn]+1</code> in mind, so why do we say <code>O(h)</code> and somewhere else <code>O(logn)</code>?</p>