OleDbData md = new OleDbData();
        md.ExecuteReader("select * from tbDept");
        XmlDocument xmlDoc = new XmlDocument();
        XmlElement root = xmlDoc.CreateElement("root");
        xmlDoc.AppendChild(root);
        while (md.Reader.Read())
        {
            int parentID = Convert.ToInt32(md.Reader["ParentID"]);
            XmlElement node = xmlDoc.CreateElement("node");
            for (int i = 0; i < md.Reader.FieldCount; i++)
                node.SetAttribute(md.Reader.GetName(i), md.Reader[i].ToString());
            if (parentID > 0)
            {
                xmlDoc.SelectSingleNode(string.Format(@"//node[@ID='{0}']", md.Reader["ParentID"])).AppendChild(node);
            }
            else
            {
                xmlDoc.DocumentElement.AppendChild(node);
            }
        }
        md.Close();
        xmlDoc.Save(Server.MapPath("~/test.xml"));