Remove customerid1 if first time selected then not display customerid1

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlCommand cmd = new SqlCommand("SELECT CustomerId, Name FROM Customers"))
            {
                cmd.CommandType = CommandType.Text;
                cmd.Connection = con;
                con.Open();
                ddlCustomers.DataSource = cmd.ExecuteReader();
                ddlCustomers.DataTextField = "Name";
                ddlCustomers.DataValueField = "CustomerId";
                ddlCustomers.DataBind();
                con.Close();
            }
        }
        ddlCustomers.Items.Insert(0, new ListItem("", ""));
    }
}