Can anybody tell me the output for this test case? The console prints nothing. 1 2 -1 3 4 -1 -1 5 6

Tree will look like:

         1

       /    

      2

    /    \

   3    4

        /   \

       5   6

As per my understanding the output should be: 1 2 3 5 6 4

But as per striver's explanation the output will be: 1 2 3 5 6