Binding a list to a DropdownList

Page Lode() 

{ 

 BindUnits(ddlUnit, "Units"); 

} 

 private void BindUnits(DropDownList ddlUnits, string lstName) 

        { 

            try 

            { 

                SPSecurity.RunWithElevatedPrivileges(delegate() 

                { 

                    using (SPSite site = new SPSite(SPContext.Current.Site.Url)) 

                    { 

                        using (SPWeb web = site.OpenWeb()) 

                        { 

                            SPList list = web.Lists[lstName]; 

  

                            ddlUnits.DataSource = list.GetItems().GetDataTable(); 

                            DataTable dt = list.GetItems().GetDataTable(); 

  

                            ddlUnits.DataValueField = "Unit_x0020_Name"; 

                            ddlUnits.DataTextField = "Unit_x0020_Name"; 

                            ddlUnits.DataBind(); 

it is the process  of placing a value to a index  

                            ListItem item = new ListItem("--Select Unit--", "0"); 

                            ddlUnits.Items.Insert(0, item); 

                            ////ddlUnits.Items.Insert(0, "--Select Unit--"); 

                            ////ddlUnits.Items.Insert( 

                            //mddlUnits.SelectedItem.Text = "0"; 

                        } 

                    } 

                }); 

            } 

            catch (Exception ex) 

            { 

                Page.ClientScript.RegisterClientScriptBlock(typeof(SPAlert), "alert", "<script language=\"javascript\">alert('" + ex.Message + "')</script>"); 

            } 

        }