1. remove Leaves of Binary Tree , like (366. Find Leaves of Binary Tree) , but need remove

follow up: 1. remove new created leaves first (after remove 4,5, we need remove 2 immediately..then 6,7 ....)
1
/ \
2 3
/ \ / \
4 5 6 7
follow up: 2 remove new created leaves last

do not know how to solve the follow up questions?
need help. Anyone can implement it ?