Fill dropDownlist in Asp.net with self reference table ?

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C#

ASP.NET

SQL

hi

i am using Asp.Net C# and i have self refernece table for category #id name Parent_id
for save category i have a text box for name and dropdownlist for parent category and on page_load i fill ddl with recursion and displayCategory() method : is there any better way to fill dropdownlist that show category ?

public DataTable getCats()
        {
            string selectQuery = "SELECT * FROM Category";
            SqlCommand cmd = new SqlCommand(selectQuery);
            return FillDataTable(cmd); 
        }
public void add_Cat(string name,int? parentId)
        {
            SqlConnection con = new SqlConnection(connectionString);

            string insertQuery = "INSERT INTO Category VALUES(@name,@parentId)";

            SqlCommand cmd = new SqlCommand(insertQuery,con);
            cmd.Parameters.AddWithValue("@name", name);
            cmd.Parameters.AddWithValue("@parentId", (parentId.HasValue) ? parentId : (object)DBNull.Value);

            try
            {
                con.Open();
                cmd.ExecuteNonQuery();
            }
            finally
            {
                con.Close();
            }


        }

protected void btnSaveCat_Click(object sender, EventArgs e)
        {
            if (String.IsNullOrWhiteSpace(txtCatName.Text))
                return;
            int? parentId = null;
            if (ddlParentCat.SelectedIndex != 0)
                parentId = int.Parse(ddlParentCat.SelectedValue);

            DBUtil DB = new DBUtil();
            DB.add_Cat(txtCatName.Text,parentId);
            bindToDDL();
        }

        private void bindToDDL()
        {
            ddlParentCat.Items.Clear();
            DBUtil DB = new DBUtil();
            DataTable dt = new DataTable();
            dt=DB.getCats();
            displayCategory(dt,null,0);
            ddlParentCat.Items.Insert(0, new ListItem("Select a category", "0"));
        }

        private void displayCategory(DataTable dt, int? id, int depth)
        {
            foreach (DataRow row in dt.Rows)
            {
                if (row["Parent_id"].ToString() == id.ToString())
                {
                    StringBuilder sb = new StringBuilder();
                    for (int i = 0; i < depth; i++)
                        sb.Append((char)0XA0);
                    ListItem ls = new ListItem(sb + row["Cat_Name"].ToString(), row["Cat_id"].ToString());
                    if (depth == 0)
                        ls.Attributes.Add("style", "color:red;");
                    ddlParentCat.Items.Add(ls);
                    displayCategory(dt, int.Parse(row["Cat_id"].ToString()), depth + 1);
                }
            }

        }