XmlReader - how to deal with large XML-Files?

I was wondering how to deal with large and complex files in a XmlReader. In my case it's a pretty complex structure and I'm not okay with handling all of this inside a single-method. This is just too dirty in my opinion - so I tried to split the method into a few smaller methods.

Therefore I started with the following code:

        // Create an XML reader for this file.
        using (var reader = XmlReader.Create(new StringReader(fileText)))
        {
          while (reader.Read()){
             if (reader.IsStartElement(){
                 switch (reader.Name){
                     case "FirstBigTag": MyMethod(reader, otherNecessaryMethods) break;
                     ....
                 }
             }

          }  
        }

Theoretically this would work fine. But I experienced some cases where this behaviour results in a wrong state.

In some cases MyMethod is parsing the correct element and then I can't clearly see "where to end" so I can't leave the method without reading the next node. This would mean that I consume an element without handling it (because this is supposed to be handled by the main-method). When I now return I get back to my "main"-method but this is the point where my consumed-string would be necessary to decide which method has to be called next. How can I solve this? Is there anything like "reader.IsEndElement" or a "reader.look" - without reading the value but foreseeing the type?

If the size of the file is too large to fit in memory, you could have the best of both worlds; read the high level nodes using XmlReader, and then use the high level abstraction as John Saunders mentioned, ie:

case "FirstBigTag": 
    using(XmlReader subReader = reader.ReadSubtree()) 
    {
        XElement element = XElement.Load(subReader);
        MyMethod(element);
    }

    break;