Pre-Order:  17 12 10  5 15 20 19 28 33 
Post-Order:  5 10 15 12 19 33 28 20 17 
In-Order:    5 10 12 15 17 19 20 28 33 
Tree minimum:  5 (iterative),  5 (recursive)
Tree maximum: 33 (iterative), 33 (recursive)