two category main categories and sub categories,

i want to display sub category into main category but here is problem of main category id ,how can it retrived into sub category please help me..

public partial class _Default : System.Web.UI.Page

{

protected CategoryManager obj;

protected SubCategoryManager obj2;

protected void Page_Load(object sender, EventArgs e)

{

obj = new CategoryManager();

obj2 = new SubCategoryManager();

Ltrmenu.Text = Menulinks();

// DataSet ds2 = obj2.AllSubCategories();

// //lbl.Text = ds2.Tables["Categories"].Rows[0]["Title"].ToString();

////lbl.Text =ds2.Tables[0].Rows[0]["Title"].GetParentRow["categoryid"].ToString();

// lbl.Text=ds2.Relations.Add(ds2.Tables["AllCategories"].Columns["Categoryid"],ds2.Tables[0].Rows[0]["Title"]);

}

public string Menulinks()

{

StringBuilder obj_html = new StringBuilder();

DataSet ds = obj.AllCategories();

DataSet ds2 = obj2.AllSubCategories();

lbl.Text = ds2.Tables[0].Rows[0]["Title"].ToString();

for (int i = 0; i < ds.Tables[0].Rows.Count; i++)

{

obj_html.Append ( "

" + ds.Tables[0].Rows[i]["Title"].ToString() + "

");

}

return obj_html.ToString();

}