The DFS method is incorrect.

[AlifBrahim]

The original output for the DFS if the node starts at 2 is as follows,
Depth-first search visitation order
[2, 5, 6, 4, 3, 8, 7, 1]

It should be,
[2, 1, 3, 5, 4, 6, 7, 8]

I've created a pull request for the correct method.