It would be 2 and 2 ways because , we are not saying that it is a complete binary tree .
In complete binary tree , we have to fill the elements from left to right , correct ?
So if the question had mentioned that it is a complete binary tree , then there would had been 2 ways and 1 ways , because the left element would had been filled in 2 ways , then for filling the right element , there had been only 1 option .
But it is a binary tree , so we can fill the right element first also , we can fill the left element first also .
Hence it can be done in both the ways , that’s why it is 2 and 2 ways .
Correct me , if i am wrong .