Use Powershell to write XML file in the given order

I have an xml file as given below

<Books>
  <Book rev="19ver" nver="1.0.0.0" >
    <Book rev="19Sub4" nver="1.4.0.250">
      <Book rev="19Sub5" nver="1.5.0.250" >
    <Book rev="19Sub5Fix1" nver="1.5.1.250" >
    </Book>
  </Book>
</Book>
<Book rev="20ver" nver="2.0.0.0" >
  <Book rev="20Sub1" nver="2.1.0.769" >
    <Book rev="20Sub1Fix7" nver="2.1.7.769"  >
    </Book>
    <Book rev="20Sub1Fix6" nver="2.1.6.769"  >
    </Book>
    <Book rev="20Sub1Fix4" nver="2.1.4.769"  >
    </Book>
    <Book rev="20Sub1Fix3" nver="2.1.3.769"  >
    </Book>
    <Book rev="20Sub1Fix2" nver="2.1.2.769"  >
    </Book>
    <Book rev="20Sub1Fix1" nver="2.1.1.769"  >
    </Book>
  </Book>
  <Book rev="20Sub3" nver="2.3.0.1111">
    <Book rev="20Sub3Fix5" nver="2.3.5.1111"  >
    </Book>
    <Book rev="20Sub3Fix4" nver="2.3.4.1111"  >
    </Book>
     <Book rev="20Sub3Fix3" nver="2.3.3.1111"  >
    </Book>
    <Book rev="20Sub3Fix2" nver="2.3.2.1111"  >
    </Book>
    <Book rev="20Sub4" nver="2.4.0.1567" >
      <Book rev="20Sub4Fix5" nver="2.4.5.1567"  >
      </Book>
      <Book rev="20Sub4Fix4" nver="2.4.4.1567"  >
      </Book>
      <Book rev="20Sub4Fix3" nver="2.4.3.1567"  >
      </Book>
      <Book rev="20Sub4Fix2" nver="2.4.2.1567"  >
      </Book>
      <Book rev="20Sub4Fix1" nver="2.4.1.1567"  >
      </Book>
    </Book>
</Book>
 </Book>
</Book>
 </Books>

I have a powershell script to add a new element inside the specified node. For example if i want to enter the element with rev "20Sub3Fix6" and nver "2.3.6.1111" inside "20Sub3" i can use the following code.

$parentXML = Select-Xml -Xml $bookInfo -XPath "//*[@rev='20Sub3']"
$bookInfo = Get-Content -Raw -Path $XMLPATH
$book = $bookInfo.CreateNode("element","book","")             
$book.SetAttribute("rev","20Sub3Fix6")
$book.SetAttribute("nver","2.3.6.1111")
$rslt = $parentXML.Node.AppendChild($book)
$bookInfo.Save($XMLPATH)

What I'm looking is that when I add a new element it should come in given order. That means "20Sub3Fix6" element should come on top of ""20Sub3Fix5" element. But now it is coming after "20Sub3Fix2".

The expcted XML format is given below

<Book rev="20Sub3" nver="2.3.0.1111">
    <Book rev="20Sub3Fix6" nver="2.3.6.1111"  >
    </Book>
    <Book rev="20Sub3Fix5" nver="2.3.5.1111"  >
    </Book>
    <Book rev="20Sub3Fix4" nver="2.3.4.1111"  >
    </Book>
     <Book rev="20Sub3Fix3" nver="2.3.3.1111"  >
    </Book>
    <Book rev="20Sub3Fix2" nver="2.3.2.1111"  >
    </Book>
    </Book>

What changes I should made in my code so that the i will get the expected XML format?