Python Program for Depth First Binary Tree Search using Recursion

class BinaryTree:
    def __init__(self, key=None):
        self.key = key
        self.left = None
        self.right = None
 
    def set_root(self, key):
        self.key = key
 
    def insert_left(self, new_node):
        self.left = new_node
 
    def insert_right(self, new_node):
        self.right = new_node
 
    def search(self, key):
        if self.key == key:
            return self
        if self.left is not None:
            temp =  self.left.search(key)
            if temp is not None:
                return temp
        if self.right is not None:
            temp =  self.right.search(key)
            return temp
        return None
 
    def depth_first(self):
        print('entering {}...'.format(self.key))
        if self.left is not None:
            self.left.depth_first()
        print('at {}...'.format(self.key))
        if self.right is not None:
            self.right.depth_first()
        print('leaving {}...'.format(self.key))
 
 
btree = None
 
print('Menu (this assumes no duplicate keys)')
print('insert <data> at root')
print('insert <data> left of <data>')
print('insert <data> right of <data>')
print('dfs')
print('quit')
 
while True:
    do = input('What would you like to do? ').split()
 
    operation = do[0].strip().lower()
    if operation == 'insert':
        data = int(do[1])
        new_node = BinaryTree(data)
        suboperation = do[2].strip().lower() 
        if suboperation == 'at':
                btree = new_node
        else:
            position = do[4].strip().lower()
            key = int(position)
            ref_node = None
            if btree is not None:
                ref_node = btree.search(key)
            if ref_node is None:
                print('No such key.')
                continue
            if suboperation == 'left':
                ref_node.insert_left(new_node)
            elif suboperation == 'right':
                ref_node.insert_right(new_node)
 
    elif operation == 'dfs':
        print('depth-first search traversal:')
        if btree is not None:
            btree.depth_first()
        print()
 
    elif operation == 'quit':
        break

Output

Menu (this assumes no duplicate keys)
insert <data> at root
insert <data> left of <data>
insert <data> right of <data>
dfs
quit
What would you like to do? insert 1 at root
What would you like to do? insert 2 left of 1
What would you like to do? insert 3 right of 1
What would you like to do? insert 4 left of 2
What would you like to do? insert 5 right of 2
What would you like to do? insert 6 left of 5
What would you like to do? insert 7 right of 5
What would you like to do? dfs
depth-first search traversal:
entering 1...
entering 2...
entering 4...
at 4...
leaving 4...
at 2...
entering 5...
entering 6...
at 6...
leaving 6...
at 5...
entering 7...
at 7...
leaving 7...
leaving 5...
leaving 2...
at 1...
entering 3...
at 3...
leaving 3...
leaving 1...
 
What would you like to do? quit