XML : XmlReader - read child

I have a trouble with reading string (xml structure) using xmlReader.

  string xml = @"  <Data>    <Prices Id="16" Code="C3" >       <Units>         <Unit Id="17"/>        </Units>     </Prices>    <Units>      <Unit Id="1" IsActive="true" />      <Unit Id="2" IsActive="true" />    </Units>   <Product Id="16" Code="C3" >        <Names>         <Name NameVersion="1" Name="C3 " />        </Names>        <Units>         <Unit Id="16"/>        </Units>   </Product>  </Data>  "    

How could I read only Element "Units" with child's id 1 and 2 ?

Actually I tried parsing this string into XDocument.

  var root = XElement.Parse(xmlFile);  var units = root.Elements("Units").FirstOrDefault();    

and it works fine but I could work with really big xml and I don't want to parse all string into XDocument. I'm looking for method when I could load partly elements from a string. Also I tried do this using XmlTextReader but this not working in my case

  using (XmlReader xmlTextReader = XmlReader.Create(new StringReader(xmlFile)))          {              if (xmlTextReader.ReadToFollowing(elementName))              {                  bool isOnNode = xmlTextReader.ReadToDescendant(elementName);                  while (isOnNode)                  {                      yield return XNode.ReadFrom(xmlTextReader) as XElement;                      if (!xmlTextReader.IsStartElement(elementName))                          isOnNode = xmlTextReader.ReadToNextSibling(elementName);                  }              }          }    

Expected output: xElement =

  <Units>      <Unit Id="1" IsActive="true" />      <Unit Id="2" IsActive="true" />    </Units>