title: EasyUI Treegrid - insert method does not update children collection
body: <p>I am using <a href="http://www.jeasyui.com/demo/main/index.php?plugin=TreeGrid&amp;theme=default&amp;dir=ltr&amp;pitem=" rel="nofollow">jQuery EasyUI treegrid</a> on a project.</p>
  
  <p>I have a tree loaded with some initial data. Afterwards, I need to insert new rows on the tree when user clicks "Add" button. The add click handler has this code and it is working somewhat as expected:</p>
  
  <pre><code>var row = $treeGrid.treegrid('getSelected');
  
  if (row) {
      var obj = {
          id: "x" + ++maxId,
          code: "x" + maxId,
          amount: 2
      };
      $treeGrid.treegrid('insert', {
              after: row.id,
              data: obj
          });
  
      $("#txtResult").text("Added a new row: " + obj.id);
  }
  </code></pre>
  
  <p>However afterwards when I check the children of the row (where a new child was added), it does not include the newly added row.</p>
  
  <p>I have setup a <a href="http://jsfiddle.net/kashiif/UKept/" rel="nofollow">jsFiddle</a> to demonstrate the issue. To reproduce it:</p>
  
  <ol>
  <li><p>Select a row at 2nd level and click Add child. A new row would be added as per the code above. A "row added" message is displayed below the buttons.</p></li>
  <li><p>Select the parent and click "Show Children" button. The children count of the selected row is shown below the buttons.</p></li>
  </ol>
  
  <p>After inserting row, I have also tried "acceptChanges" of treegrid but it still does not solve the problem.</p>
  
  <p><strong>UPDATE</strong>: As per @saigitha-vijay answer, it looks like using append method correctly updates the underlying model (<a href="http://jsfiddle.net/n4yMy/2/" rel="nofollow">jsFiddle</a>) however it always adds the new row as last child. Is there anyway to add new row at a particular position?</p>