Test 1 The ceiling of Jul 02 12:00 is NULL Test 2 Apr 14 12:00 (height: 2) ┝━╸L: Feb 17 12:00 (height: 1) │ ┝━╸L: Jan 04 12:00 (height: 0) │ ┕━╸R: Mar 29 12:00 (height: 0) ┕━╸R: Jun 06 12:00 (height: 1) ┝━╸L: May 19 12:00 (height: 0) ┕━╸R: Jul 07 12:00 (height: 0) The ceiling of Jan 01 12:00 is Jan 04 12:00 The ceiling of Jan 09 12:00 is Feb 17 12:00 The ceiling of Mar 15 12:00 is Mar 29 12:00 The ceiling of Apr 01 12:00 is Apr 14 12:00 The ceiling of Apr 27 12:00 is May 19 12:00 The ceiling of May 30 12:00 is Jun 06 12:00 The ceiling of Jun 22 12:00 is Jul 07 12:00 The ceiling of Jul 12 12:00 is NULL