private IEnumerator Start()
    {
        UnityTaskScheduler.Initialize();

        var task = Task.Run(() => print("First action."))
                   .ContinueWith(t => print("wait for click"))
                   .ContinueWith(WaitForClick()) // <- IEnumerator
                   .ContinueWith(new WaitForSeconds(1))
                   .ContinueWith(t =>
        {
            print("Second action.");
        })
                   .ContinueWith(new WaitForSeconds(1))
                   .ContinueWith(t =>
        {
            print("Third action.");
        });

        yield return(task);

        print("All done!");
    }