If we take the tree as in Faland's comment.

      1
     / \
    2   3
   / \
  4   5
       \
        6
         \
          7

The answer for which the compiler successfully runs the test is 4-2-1-3-7

and for

      1
     / \
    2   3
   / \
  4   5
     / 
    6
   /
  7
 /
8 

output is 8-4-2-1-3 which compiler accepts.

You may refer geeks for geeks for the top view.