You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. Each node has a next pointer. Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to None.

• The root of a perfect binary tree.

Input: root = [1, 2, 3, 4, 5, 6, 7]
Output: [1, #, 2, 3, #, 4, 5, 6, 7, #]