{|pre-order|:{1, 2, 4, 7, 5, 3, 6, 8, 9},
|in-order|:{7, 4, 2, 5, 1, 8, 6, 9, 3},
|post-order|:{7, 4, 5, 2, 8, 9, 6, 3, 1},
|level-order|:{1, 2, 3, 4, 5, 6, 7, 8, 9}}