Infopath 2010 Drop-Down List Box (Get choices from fields in this form)

Binding Dropdown in infopath form load without using Data Connections ( Dropdown [Get choices from fields in this form]) using code behind.

• Go to Infopath form, Add one Group (like test),set properties -check (Repeating).
• Add two fields (like test_displayname and test_value) under Group.
• Add one Dropdown,set properties (Get choices from fields in this form).
• set the value as Group [like test_displayname and test_value].
• go to on form load events write the code.

public void FormEvents_Loading(object sender, LoadingEventArgs e)
        {
            XPathNavigator myRootNode = MainDataSource.CreateNavigator();
            XPathNavigator userNode = myRootNode.SelectSingleNode("/my:myFields/my:test", NamespaceManager);
            using (SPSite site = new SPSite(SPContext.Current.Site.Url))
            {
                using (SPWeb web = site.OpenWeb())
                {
                    SPList userlist = web.Lists["Departments"];
                     SPListItemCollection usercollection = userlist.GetItems();

                    if (usercollection.Count > 0)
                    {
                        foreach (SPListItem item in usercollection)
                        {
                            XPathNavigator newNode = null;
                            newNode = userNode.Clone();
                            newNode.SelectSingleNode("/my:myFields/my:test/my:test_displayname", this.NamespaceManager).SetValue(item.Title);
                            newNode.SelectSingleNode("/my:myFields/my:test/my:test_value", this.NamespaceManager).SetValue(item.Title);
                            userNode.InsertAfter(newNode);
                            newNode = null;
                        }
                        userNode.DeleteSelf();
                        userNode = null;
                    }
                }
            }