title: Construct binary tree of pre-order, post-order and in-order expression
body: <p>I searched internet and "you tube" but I didn't find any good tutorial for this.
  How can I draw corresponding "binary tree" of a given expression in “postfix”?</p>
  
  <p>And how would this expression look in infix and prefix?</p>
  
  <p>I don’t know how I should do this step by step :(</p>
  
  <p>18    5    1    +     /    4     *     3     5    18     6     /     -     +     -</p>
  
  <p>Note:</p>
  
  <p>The rule for drawing pre-order, post-order and in-order is:
  1. pre-order traversal: root, left, right
  2. post-order traversal: left, right, root
  3. in-order traversal: left root, right</p>
  
  <p>Please I need it for exam</p>