diff --git a/data_structures/persistent_segment_tree.py b/data_structures/persistent_segment_tree.py
index 074e137bb..05194fa20 100644
--- a/data_structures/persistent_segment_tree.py
+++ b/data_structures/persistent_segment_tree.py
@@ -1,11 +1,13 @@
 from __future__ import annotations
 
+
 class Node:
     def __init__(self, value: int = 0) -> None:
         self.value: int = value
         self.left: Node | None = None
         self.right: Node | None = None
 
+
 class PersistentSegmentTree:
     def __init__(self, arr: list[int]) -> None:
         self.n: int = len(arr)
@@ -81,7 +83,9 @@ class PersistentSegmentTree:
             new_node.left = node.left  # Ensure left node is the same as the original
             new_node.right = self._update(node.right, mid + 1, end, index, value)
 
-        new_node.value = new_node.left.value + (new_node.right.value if new_node.right else 0)
+        new_node.value = new_node.left.value + (
+            new_node.right.value if new_node.right else 0
+        )
 
         return new_node
 
@@ -97,7 +101,7 @@ class PersistentSegmentTree:
         >>> version_1 = pst.update(0, 1, 5)  # Update index 1 to 5
         >>> pst.query(version_1, 0, 3)  # Sum of all elements in new version
         13
-        >>> pst.query(version_1, 1, 2)  # Sum of elements at index 1 and 2 
+        >>> pst.query(version_1, 1, 2)  # Sum of elements at index 1 and 2
         8
         """
         return self._query(self.roots[version], 0, self.n - 1, left, right)
@@ -120,12 +124,15 @@ class PersistentSegmentTree:
         if left <= start and right >= end:
             return node.value
         mid = (start + end) // 2
-        return (self._query(node.left, start, mid, left, right) +
-                self._query(node.right, mid + 1, end, left, right))
+        return self._query(node.left, start, mid, left, right) + self._query(
+            node.right, mid + 1, end, left, right
+        )
+
 
 # Running the doctests
 if __name__ == "__main__":
     import doctest
+
     print("Running doctests...")
     result = doctest.testmod()
     print(f"Ran {result.attempted} tests, {result.failed} failed.")