title: Populate Tree using data from ArrayCollection
body: <p>Let's say I had an ArrayCollection like this:</p>
  
  <pre><code>        public var ac:ArrayCollection= new ArrayCollection([
              {item:"dog", group:"Animals"},
              {item:"orange", group:"Fruits"}, 
              {item:"cat", group:"Animals"},
              {item:"apple", group:"Fruits"}
              ]);
  </code></pre>
  
  <p>How would I create a Tree component in Flex 3 that uses the groups as nodes, with the appropriate items listed under each node?</p>