Adding a Node in the Specified Node's Child Nodes with AddBeforeSelf

   
 
using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using System.Xml;
using System.Xml.Linq;
public class MainClass {
    public static void Main() {
        XDocument xDocument = new XDocument(
          new XElement("Books",
            new XElement("Book",
              new XAttribute("type", "Author"),
              new XElement("FirstName", "A"),
              new XElement("LastName", "B"))));
        xDocument.Element("Books").Add(
          new XElement("Book",
            new XAttribute("type", "Author"),
            new XElement("FirstName", "E"),
            new XElement("LastName", "B")));

        xDocument.Element("Books").
          Elements("Book").
          Where(e => ((string)e.Element("FirstName")) == "E").
          Single<XElement>().AddBeforeSelf(
            new XElement("Book",
              new XAttribute("type", "Reviewer"),
              new XElement("FirstName", "F"),
              new XElement("LastName", "F")));
        Console.WriteLine(xDocument);
    }
}