Construct binary tree
root = Node ( 1 ) NEW_LINE root . left = Node ( 2 ) NEW_LINE root . left . left = Node ( 4 ) NEW_LINE root . left . left . left = Node ( 21 ) NEW_LINE root . left . right = Node ( 5 ) NEW_LINE root . left . right . right = Node ( 8 ) NEW_LINE root . right = Node ( 3 ) NEW_LINE root . right . left = Node ( 6 ) NEW_LINE root . right . right = Node ( 7 ) NEW_LINE root . right . right . right = Node ( 19 ) NEW_LINE