WPF

using (FileStream stream = new FileStream("text.xaml", FileMode.Create, FileAccess.Write))
{
  XmlWriterSettings settings = new XmlWriterSettings();
                settings.Indent = true;
                settings.ConformanceLevel = ConformanceLevel.Auto;
                XmlWriter writer = XmlWriter.Create(stream, settings);
                XamlDesignerSerializationManager manager = new XamlDesignerSerializationManager(writer);
                manager.XamlWriterMode = XamlWriterMode.Expression;
                XamlWriter.Save(Viewport, manager);
            }

ModelVisual3D model = new ModelVisual3D();
model.Content = new GeometryModel3D(MeshPrimitives.Box(10, 10, 10), new DiffuseMaterial(new SolidColorBrush(Colors.Red)));
model.Transform = new TranslateTransform3D(new Vector3D(0, 20, 0));
model.SetValue(FrameworkElement.NameProperty, "SomeBox");

Viewport.Children.Add(model);