Microsoft : find the next biggest node in a BST

Write a function that, given a binary search tree and a value,
will find the next biggest node value in the tree

Find this node and record its parent nodes in the path, stores them in a stack says S.
If this node got a right child, the left most node of the left tree of this node
is the next biggest one.
If no right child existed, pop the parent node within stack S one by one until you see
the first node with its value bigger than the given node. This node is the one you want to find.

什么叫next biggest value？那不就是最右边的了么？