Design a Data Structure of size O(n) (e.g. of Given Tree Size n) so that you can answer any such query in O(log n) time.

Given a rooted tree of size n . You receive a series of online queries : "Give nearest common ancestor of u,v " . Your objective is to preprocess the tree in O(n) time to get a data structure of size O(n) so that you can answer any such query in O(log n) time.