如何向C#中的数据集Writexml生成的XML添加额外信息？

DataTable extraInfoTable = new DataTable("ExtraInfo");
extraInfoTable.Columns.Add("Key", typeof(string));
extraInfoTable.Columns.Add("Value", typeof(string));

DataRow extraInfoRow = extraInfoTable.NewRow();
extraInfoRow["Key"] = "ExtraInfo1";
extraInfoRow["Value"] = "ExtraInfo1 Value";
extraInfoTable.Rows.Add(extraInfoRow);

DataSet dataSet = new DataSet();
dataSet.Tables.Add(extraInfoTable);

using (FileStream fs = new FileStream("output.xml", FileMode.Create))
{
    dataSet.WriteXml(fs);
}

DataTable existingTable = dataSet.Tables["ExistingTable"];

DataColumn extraInfoColumn = new DataColumn("ExtraInfo", typeof(string));
existingTable.Columns.Add(extraInfoColumn);

foreach (DataRow row in existingTable.Rows)
{
    row["ExtraInfo"] = "ExtraInfo Value";
}