This is probably the last post about jqGrid. TreeGrid is quite cool and very easy to use feature. It supports both the Nested Set model and the Adjacency model. I'm going to show only the Adjacency model, but all the differences lies in data handling.
We will start with jqGrid initlization function:

<script type="text/javascript">
  $(document).ready(function() {
    $('#jqgTreeGrid').jqGrid({
      //enable TreeGrid
      treeGrid: true,
      //set TreeGrid model
      treeGridModel: 'adjacency',
      //set expand column
      ExpandColumn: 'Name',
      //url from wich data should be requested
      url: '/Home/FilesAdjacencyTreeGridData/',
      //type of data
      datatype: 'json',
      //url access method type
      mtype: 'POST',
      //columns names
      colNames: ['Path', 'Name', 'CreationTime', 'LastAccessTime', 'LastWriteTime'],
      //columns model
      colModel: [
                  { name: 'Path', index: 'Path', width: 1, hidden: true, key: true },
                  { name: 'Name', index: 'Name', align: 'left' },
                  { name: 'CreationTime', index: 'CreationTime', align: 'left' },
                  { name: 'LastAccessTime', index: 'LastAccessTime', align: 'left' },
                  { name: 'LastWriteTime', index: 'LastWriteTime', align: 'left' }
                ],
      //pager for grid
      pager: $('#jqgpTreeGrid'),
      //grid width
      width: 'auto',
      //grid height
      height: 'auto'
    });
  });
</script>

As you can see, the grid is configured to perform POST request. If the request is for child node, it will have three additional parameters: nodeid - the id of the currently expanded node, parentid - the parent id of the currently expanded node, n_level - the level value of the currently expanded node. We also need to add corresponding fields to every cell array in rows array. Here is a simple example:

/// <summary>
/// Provides json data for TreeGrid in adjacency mode
/// </summary>
/// <param name="postData">POST parameters collection</param>
/// <returns></returns>
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult FilesAdjacencyTreeGridData(FormCollection postData)
{
  DirectoryInfo root = null;
  //Checking if we are expanding existing node
  if (postData.AllKeys.Contains("nodeid"))
    root = new DirectoryInfo(postData["nodeid"]);
  else
    root = new DirectoryInfo(@"D:\Books\");
  //Getting childrens
  var children = from child in root.GetFileSystemInfos()
                 orderby child is DirectoryInfo descending
                 select child;

  //Preparing result
  var filesData = new
  {
    page = 1,
    total = 1,
    records = children.Count(),
    rows = (from child in children
            select new
            {
              //table of cells values
              cell = new object[] {
                                    child.FullName,
                                    child.Name,
                                    child.CreationTime.ToString(),
                                    child.LastAccessTime.ToString(),
                                    child.LastWriteTime.ToString(),
                                    //Level - based on '\' count
                                    ((from backslash in child.FullName
                                    where backslash == '\\'
                                    select backslash).Count() - 2),
                                    //Parent id
                                    root.FullName == @"D:\Books\" ? null : root.FullName,
                                    //Is not expandable
                                    child is FileInfo,
                                    //Is expanded
                                    false
                                  }
            }
           ).ToArray()
  };

  //Returning json data
  return Json(filesData);
}

Screenshot of our sample at work (you can download source code here):