public class SubtypeGroupLayerCreationParams : LayerCreationParams 

var subtypeGroupLayerCreateParam = new SubtypeGroupLayerCreationParams
(
    new Uri(@"c:\data\SubtypeAndDomain.gdb\Fittings")
);

// Define Subtype layers
//At 2.x - var rendererDefn1 = new UniqueValueRendererDefinition(new string[] { "type" });
var rendererDefn1 = new UniqueValueRendererDefinition(new List<string> { "type" });
var renderDefn2 = new SimpleRendererDefinition()
{
  SymbolTemplate = SymbolFactory.Instance.ConstructPointSymbol(
          CIMColor.CreateRGBColor(255, 0, 0), 8, SimpleMarkerStyle.Hexagon).MakeSymbolReference()
};
subtypeGroupLayerCreateParam.SubtypeLayers = new List<SubtypeFeatureLayerCreationParams>()
{
  //define first subtype layer with unique value renderer
  //At 2.x - new SubtypeFeatureLayerCreationParams(new UniqueValueRendererDefinition(new string[] { "type" }), 1),
  new SubtypeFeatureLayerCreationParams(new UniqueValueRendererDefinition(new List<string> { "type" }), 1),

  //define second subtype layer with simple symbol renderer
  new SubtypeFeatureLayerCreationParams(renderDefn2, 2)
};

// Define additional parameters
//At - 2.x subtypeGroupLayerCreateParam.DefinitionFilter = new CIMDefinitionFilter()
//{
//  Name = "IsActive",
//  DefinitionExpression = "Enabled = 1"
//};
subtypeGroupLayerCreateParam.DefinitionQuery = new DefinitionQuery(whereClause: "Enabled = 1", name: "IsActive");
subtypeGroupLayerCreateParam.IsVisible = true;
subtypeGroupLayerCreateParam.MinimumScale = 50000;

SubtypeGroupLayer subtypeGroupLayer2 = LayerFactory.Instance.CreateLayer<SubtypeGroupLayer>(
              subtypeGroupLayerCreateParam, MapView.Active.Map);