title: converting a binary tree into List<List<Node>>
body: <p>IS my algorithm correct?</p>
  
  <pre><code>List&lt;List&lt;Node&gt; &gt; ol = new ArrayList&lt;List&lt;Node&gt;&gt;();
  build(root,0)
  
  void build (Node node,int level)
  { 
   if(node==null)
      return;
    List&lt;Node&gt; il;
    if(ol.size() &lt; level){
     il =  new ArrayList&lt;Node&gt;(); 
    }else{
    il= ol.get(level);
    }
  
  il.add(node);
  ol.put(level,il);
   build(node.left, level+1);
   build(node.right,level+1);
  }
  </code></pre>