pre-order traversal, with recursion:
35 28 20 25 23 26 30 60 70 65 64 68
pre-order traversal, without recursion:
35 28 20 25 23 26 30 60 70 65 64 68
in-order traversal, with recursion:
20 23 25 26 28 30 35 60 64 65 68 70
in-order traversal, without recursion:
28 30 35 60 65 68 70