Something

public void LoadFromXML(XmlTextReader reader)
        {
            cameras.Clear();
            lights.Clear();
            objects.Clear();

            reader.ReadStartElement("Scene");
            //Read All Cameras
            reader.ReadStartElement("Cameras");

            while(reader.IsStartElement("Camera"))
            {
                RTCamera camera = new RTCamera();
                camera.ReadFromXML(reader);
                cameras.Add(camera);
            }

            reader.ReadEndElement(); //Cameras

            reader.ReadStartElement("Lights");

            while (reader.IsStartElement("Light"))
            {
                reader.ReadStartElement("Light");
                RTLight light;

                if (reader.IsStartElement("PointLight"))
                {
                    light = new RTPointLight();
                    light.ReadFromXML(reader);
                }                
            }

            reader.ReadEndElement(); //Lights

            reader.ReadEndElement(); //Scene
        }