C#

[XmlRoot]
public class AList
{
   public List<B> ListOfBs {get; set;}
}

public class B
{
   public string BaseProperty {get; set;}
}

public class C : B
{
    public string SomeProperty {get; set;}
}

public class Main
{
    public static void Main(string[] args)
    {
        var aList = new AList();
        aList.ListOfBs = new List<B>();
        var c = new C { BaseProperty = "Base", SomeProperty = "Some" };
        aList.ListOfBs.Add(c);

        var type = typeof (AList);
        var serializer = new XmlSerializer(type);
        TextWriter w = new StringWriter();
        serializer.Serialize(w, aList);
    }    
}

TypeDescriptor.AddAttributes(typeof(AList), new[] { new XmlIncludeAttribute(c.GetType()) });

var type = typeof (AList);

FileStream source = new FileStream(@"..\HtmlPages\supportHtml.html", FileMode.Open, FileAccess.Read);
webBrowser.DocumentStream = source;

 <?xml version="1.0" encoding="windows-1251" ?> 
 <MSGTaggingConfig version="1.0">
 <AssetClassConfiguration>
 <GlobalTypes>
  <FieldType id="F_TICKER" name="Ticker/Alias" color="#FF6600" type="S" output="false" description="Ticker Description" /> 
  <FieldType id="F_COUPON" name="Coupan/Alias" color="#FF3300" type="S" output="false" description="Ticker Description" /> 
  <FieldType id="F_BID" name="Bid Price" color="#FF9900" type="S" output="false" description="Bid Price Description" /> 
  <FieldType id="F_ASK" name="Ask Price" color="#FFCC00" type="S" output="false" description="Ask Price Description" /> 
  <FieldType id="F_TRENOR" name="Trenor" color="#FFCC33" type="S" output="false" description="Trenor Description" /> 
  <FieldType id="F_MATURITY" name="Maturity" color="#FFCC66" type="S" output="false" description="Maturity Description" /> 
  <FieldType id="F_ASSETQUALIFIER" name="Asset Qualifier" color="#CC9933" type="S" output="false" description="Asset Qualifier Description" /> 
  </GlobalTypes>
 <AssetClass id="AC_CDS" name="CDS" description="CDS Asset Class Description">
  <FieldType id="SECURITY" name="Security" color="#CC9900" type="C" output="true" description="Security Description" /> 
  <FieldType id="F_New" name="New Name" color="#008040" type="S" output="True" description="New Desc" /> 
  <FieldType id="F_New" name="New Name" color="Green" type="S" output="True" description="New desc" /> 
  <FieldType id="F_New" name="New Name" color="#80FF00" type="S" output="True" description="New Description" /> 
  </AssetClass>
</AssetClassConfiguration>
  </MSGTaggingConfig>