title: Time complexity, binary (search) tree
body: <p>assume I have a complete binary tree up-to a certain depth <em>d</em>. What would the time complexity be to traverse (pre-order traversal) this tree.</p>
  
  <p>I am confused because I know that the amount of nodes in the tree is 2^d, so therefore the time complexity would be <code>BigO(2^d)</code> ? because the tree is growing exponentially. </p>
  
  <p>But, upon research on the internet, Everyone states that's traversal is <code>BigO(n)</code> where n is the number of elements (which would be <code>2^d</code> in this case), not <code>BigO(2^d)</code>, what am I missing?</p>
  
  <p>thanks  </p>