N Level TreeView

CatagoryID ParentCatagoryID

1 --

2 --

4 2

5 2

6 1

7 --

8 4

9 2

<asp:TreeView ID="TreeView1" runat="server" OnTreeNodePopulate="TreeView_TreeNodePopulate" />

    protected void Page_Load(object sender, EventArgs e)
   {
       if (!IsPostBack)
       {
           PopulateRootLevel();
       }
   }

   private void PopulateRootLevel()
   {
       SqlConnection objConn = new SqlConnection(ConnectionString);
        SqlCommand objCommand = new SqlCommand("SELECT sc.CatagoryID, sc.ParentCatagoryID,(SELECT COUNT(*) FROM yourtable WHERE (ParentCatagoryID= sc.CategoryID)) AS childnodecount FROM yourtable AS sc", objConn);
        SqlDataAdapter da = new SqlDataAdapter(objCommand);DataTable dt = new DataTable();
        da.Fill(dt);        PopulateNodes(dt, TreeView1.Nodes);
   }

   private void PopulateNodes(DataTable dt, TreeNodeCollection nodes)
   {
       foreach (DataRow dr in dt.Rows)
       {
           TreeNode tn = new TreeNode();
           tn.Value = dr["CatagoryId"].ToString();
           tn.Text = dr["CatagoryId"].ToString();
           nodes.Add(tn);
           //If node has child nodes, then enable on-demand populating
           tn.PopulateOnDemand = ((int)(dr["childnodecount"]) > 0);
       }
   }

   protected void TreeView_TreeNodePopulate(object sender, TreeNodeEventArgs e)
   {
       int ParentCatagoryID= Int32.Parse(e.Node.Value);
       PopulateSubLevel(ParentCatagoryID, e.Node);
   }

   private void PopulateSubLevel(int ParentCatagoryID, TreeNode parentNode)
   {
       //Your sublevel Datatable ie. dtSub
       PopulateNodes(dtSub, parentNode.ChildNodes);
   }