I can't pass the test case [1,2,3,4,5], my output is 6, but expected one is 4. I even don't know what the tree will be look like by giving me [1,2,3,4,5].

Pleas help me to find my mistake. Thank you!

```
class Solution(object):
def sumOfLeftLeaves(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if not root:
return 0
return self.leftLeaves(root.left, True) + self.leftLeaves(root.right, False)
def leftLeaves(self, root, is_left):
if not root:
return 0
it_val = root.val if is_left else 0
return it_val + self.leftLeaves(root.left, True) + self.leftLeaves(root.right, False)
```