title: How to sort Guava's MultiMap only by keys?
body: <p>I have MultiMap from Guava library. I want to sort it only by keys. I have tried:</p>
  
  <pre><code>Multimap&lt;String, MyObj&gt; sortedMultiMap =
      TreeMultimap.create(Ordering.from(new Comparator&lt;String&gt;() {
          @Override
          public int compare(String lhs, String rhs) {
              //my comparison here
          }
      }), Ordering.natural());//i want not to sort values at all,MyObj doesn't implement Comparable
  sortedMultiMap.putAll(notSortedMultiMap);
  </code></pre>
  
  <p>But as you can see, <em>TreeMultiMap.create</em> method has 2 arguments - comparators for keys and values. How i can sort MultiMap only by keys?</p>