XML文件带有命名空间读取所有节点

//批量处理节点结构不一样的XML，获取最终节点的并集，建立模型，进行入库操作。
private void button1_Click(object sender, EventArgs e)
        {
            FileList = GetAllFiles(new System.IO.DirectoryInfo(@"C:\Users\PC_YUE\Desktop\测试XML"));
           
            for (int i = 0; i < FileList.Count; i++)
            {
                //使用XmlDocument读取XML
                XmlDocument xdoc = new XmlDocument();
                //相对路径
                xdoc.Load(@FileList[i].FilePath);
                //第一个节点
                XmlNode xnode = xdoc.DocumentElement.FirstChild;
                XmlNode root = xdoc.DocumentElement;
                XmlNamespaceManager nsp = new XmlNamespaceManager(xdoc.NameTable);
                nsp.AddNamespace("xocs", "http://www.elsevier.com/xml/xocs/dtd");
                XmlNodeList a = root.SelectNodes("child::xocs:meta", nsp);
                XmlNodeList xnlist = a[0].ChildNodes;

                foreach (XmlNode el in xnlist)
                {
                    nodeList.Add(el.Name);
                }
                i++;
            }
            var list = nodeList.Distinct<string>().ToList(); 
            for (int j = 0; j < list.Count; j++)
            {
                ListViewItem lvi = new ListViewItem(j.ToString());
                lvi.SubItems.Add(list[j]);

                listView1.Items.Add(lvi);
            }
        }
 /// <summary>
        /// 定义Xml模型-文件所在路径和文件名
        /// </summary>
        public class FileInformation
        {
            public string FileName { get; set; }
            public string FilePath { get; set; }
        }
        static List<FileInformation> FileList = new List<FileInformation>();

        public static List<FileInformation> GetAllFiles(DirectoryInfo dir)
        {
            FileInfo[] allFile = dir.GetFiles();
            foreach (FileInfo fi in allFile)
            {
                FileList.Add(new FileInformation { FileName = fi.Name, FilePath = fi.FullName });
            }
            DirectoryInfo[] allDir = dir.GetDirectories();
            foreach (DirectoryInfo d in allDir)
            {
                GetAllFiles(d);
            }
            return FileList;
        }

        List<string> nodeList = new List<string>();