Load treelistview from datasource with hardcoded root nodes on treelistview

//This demo is show the pc file system as a tree

 public void LoadTree(TreeNode parentNode)
{
    string path = parentNode.Tag as string;
    foreach (string drv in System.IO.Directory.GetFiles(path))
    {
        TreeNode driverNode = new TreeNode(drv);
        driverNode.Tag = drv;
        driverNode.Nodes.Clear();
        parentNode.Nodes.Add(driverNode);

    }

    foreach (string drv in System.IO.Directory.GetDirectories(path))
    {
        TreeNode driverNode = new TreeNode(drv);
        driverNode.Tag = drv;
        driverNode.Nodes.Clear();
        parentNode.Nodes.Add(driverNode);

    }
 }


 private void button1_Click(object sender, EventArgs e)
 {
     foreach (System.IO.DriveInfo drv in System.IO.DriveInfo.GetDrives())
     {
         TreeNode driverNode = new TreeNode(drv.Name);
         driverNode.Tag = drv.Name;
         driverNode.Nodes.Clear();
         LoadTree(driverNode);
         this.treeView1.Nodes[0].Nodes.Add(driverNode);
     }
}

foreach (DataRow dr in ds.Tables["groupmasterdetails"].Rows)
            {                
                TreeNode tn = new TreeNode(dr["GroupDesc"].ToString());
                foreach (DataRow drChild in dr.GetChildRows("test"))
                {
                    TreeNode ctn=new TreeNode(drChild["GroupDesc"].ToString());
                    foreach (DataRow drgrandChild in drChild.GetChildRows("test1"))
                    {
                        TreeNode gctn = new TreeNode(drgrandChild["AccountDesc"].ToString());
                        ctn.Nodes.Add(gctn);
                    }
                    tn.Nodes.Add(ctn);
                }
                treeView1.Nodes[0].Nodes.Add(tn);            
            }