# Learn Tree Traversal by Building a Binary Search Tree - Step 62

### Tell us what’s happening:

I can’t figure out the last step.
I don’t understand where is my mistake

``````
class TreeNode:

def __init__(self, key):
self.key = key
self.left = None
self.right = None

def __str__(self):
return str(self.key)

class BinarySearchTree:

def __init__(self):
self.root = None

def _insert(self, node, key):
if node is None:
return TreeNode(key)

if key < node.key:
node.left = self._insert(node.left, key)
elif key > node.key:

node.right = self._insert(node.right, key)
return node

def insert(self, key):
self.root = self._insert(self.root, key)

def _search(self, node, key):
if node is None or node.key == key:
return node
if key < node.key:
return self._search(node.left, key)
return self._search(node.right, key)

def search(self, key):
return self._search(self.root, key)

def _delete(self, node, key):
if node is None:
return node
if key < node.key:
node.left = self._delete(node.left, key)
elif key > node.key:
node.right = self._delete(node.right, key)
else:
if node.left is None:
return node.right
elif node.right is None:
return node.left

node.key = self._min_value(node.right)
node.right = self._delete(node.right, node.key)

return node

def delete(self, key):
self.root = self._delete(self.root, key)

def _min_value(self, node):
while node.left is not None:
node = node.left
return node.key

def _inorder_traversal(self, node, result):
if node:
self._inorder_traversal(node.left, result)
result.append(node.key)
self._inorder_traversal(node.right, result)

def inorder_traversal(self):
result = []
self._inorder_traversal(self.root, result)
return result

# User Editable Region

bst = BinarySearchTree()
nodes = [50, 30, 20, 40, 70, 60, 80]

for node in nodes:
bst.insert(node)

print('Search for 80:', bst.search(80))
print("Inorder traversal:", bst.inorder_traversal())

bst.delete(40)

print("Search for 40:", bst.search(40))
print('Inorder traversal after deleting 40:', bts.inorder_traversal())

# User Editable Region

``````

User Agent is: `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36`

### Challenge Information:

Learn Tree Traversal by Building a Binary Search Tree - Step 62

small typo in the name of the class

how could I not see that ?!

Thanks a lot

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