@ABKUNDAN Since its the Array representation of Binary Tree which has the very drawback that unnecessary array space is wasted if the tree is any normal Binary tree (i.e worst case 2^{n}-1) and not a Complete Binary tree (where in CBT its actually n).
So in such cases (any normal Binary tree), we instead prefer Linked List Representation of Binary Tree which occupies less space comparatively.
Though random access is not possible with Linked List as traversing is done via pointers and Arrays permits the use of formulae to fetch any node randomly, so Array leads the choice when we have complete Binary tree.