###### Python Function to Find the Maximum Element in a Binary Search Tree

A binary search tree (BST) is a special type of binary tree where each node has a value greater than all values in its left subtree and less than all values in its right subtree. To find the maximum element in a BST, one can simply traverse the tree to the rightmost node, as the maximum value is always located there.
Here's a Python function to achieve this:
class TreeNode:
def **init**(self, value):
self.value = value
self.left = None
self.right = None
def find_maximum(root):
if root is None:
raise ValueError("The tree is empty.")
current = root
while current.right is not None:
current = current.right
return current.value
# Example usage:
if **name** == "**main**":
# Creating a sample binary search tree
root = TreeNode(10)
root.left = TreeNode(5)
root.right = TreeNode(15)
root.right.right = TreeNode(20)
max_value = find_maximum(root)
print("The maximum value in the BST is:", max_value) # Output: 20

###### Explanation of the Code

1. **TreeNode Class**: This class defines the basic structure of a node in a binary search tree, with *value*, *left*, and *right* attributes.
2. **find_maximum Function**:
- The function takes the root of the BST as an argument.
- Before proceeding, it checks if the tree is empty, raising a *ValueError* if it is.
- A loop traverses the tree to the right child of the current node until there are no more right children. The rightmost node is the one containing the maximum value.
3. **Example Usage**:
- An example tree is created, and the *find_maximum* function is called to retrieve and print the maximum element in the BST.
###### Benefits of this Approach

- **Efficiency**: The function efficiently finds the maximum element in O(h) time, where h is the height of the tree.
- **Simplicity**: The iterative traversal is straightforward, making it easy to read and maintain.
This implementation can be used as part of larger programs that involve operations on binary search trees, ensuring that users can quickly and reliably obtain the maximum value present in their data structure.