Why facing error due to spacing?

class BinaryTree:
def __init__(self, root):
self.key = root
self.left_child = None
self.right_child = None

def insert_left(self, new_node):
if (self.left_child is None):
self.left_child = BinaryTree (new_node) # face run-time error here?
else:
t = BinaryTree(new_node)
t.left_child = self.left_child
self.left_child = t
def insert_right(self, new_node):
if self.right_child is None:
self.right_child = BinaryTree(new_node)
else:
t = BinaryTree(new_node)
t.right_child = self.right_child
self.right_child = t
def get_right_child(self):
return self.right_child
def get_left_child(self):
return self.left_child
def set_root_val(self, obj):
self.key = obj
def get_root_val(self):
return self.key r

Have formatted code at:
https://ideone.com/p4iV9N

The run-time error occurs at line #10.

It is stated as:

Traceback (most recent call last):
File "/usr/lib/python3.7/py_compile.py", line 143, in compile
_optimize=optimize)
File "<frozen importlib._bootstrap_external>", line 791, in source_to_code
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "./prog.py", line 10
self.left_child = BinaryTree (new_node)
^
TabError: inconsistent use of tabs and spaces in indentation