For the purposes of the foregoing, a trust or portion of a trust is revocable if it is subject to a power, exercisable immediately or at any future time, to revest title in the person whose property constitutes such trust or portion of a trust, and a trust or portion of a trust becomes irrevocable when the possibility that such power may be exercised has been terminated.
N.Y. Gen. City Law § 25-A-6