Identify balanced and full binary search tree insert order
Keep trying.  Try a recursive algorithm.  You know that the root needs to be 8.  You should be able to infer what numbers need to go in the left subtree of the root.  What order should you insert those numbers in, to ensure that the left subtree results in a full and balanced binary tree?  Hmm, does that resemble a problem you've seen before?  You should be able to take it from there.