In$-$order Successor in BST

Objective:

Implement a function to find the in$-$order successor of a given node in a Binary Search Tree $($BST$).$ The in$-$order successor of a node $\backslash (\backslash$boldsymbol$\{$n$\}\backslash )$ is the node with the smallest key greater than $\backslash (\backslash$boldsymbol$\{$n$\}\backslash ).$val.

Problem Statement:

Given a binary search tree and a node p in the tree, write a function to find the in$-$order successor of that node. If the node has no in$-$order successor, return None.

Example:

$11\text{'}$s successor is $12$

$20\text{'}$s successor is $30$

$2\text{'}$s successor is $7$

$40\text{'}$s successor is None