ApiRouter side by side with standard route.

gistfile1.txt

config.Routes.MapHttpRoute(
                name: "TreeApi",
                routeTemplate: "tree/{*path}",
                defaults: null,
                constraints: null,
                handler: new ApiRouter("", new Uri("http://localhost:64921/tree")).To<FooController>());

config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );