diff --git a/data_structures/binary_tree/segment_tree.py b/data_structures/binary_tree/segment_tree.py
index 5f822407d..3b0b32946 100644
--- a/data_structures/binary_tree/segment_tree.py
+++ b/data_structures/binary_tree/segment_tree.py
@@ -3,7 +3,8 @@ import math
 
 class SegmentTree:
     def __init__(self, a):
-        self.N = len(a)
+        self.A = a
+        self.N = len(self.A)
         self.st = [0] * (
             4 * self.N
         )  # approximate the overall size of segment tree with array N
@@ -11,14 +12,32 @@ class SegmentTree:
             self.build(1, 0, self.N - 1)
 
     def left(self, idx):
+        """
+        Returns the left child index for a given index in a binary tree.
+
+        >>> s = SegmentTree([1, 2, 3])
+        >>> s.left(1)
+        2
+        >>> s.left(2)
+        4
+        """
         return idx * 2
 
     def right(self, idx):
+        """
+        Returns the right child index for a given index in a binary tree.
+
+        >>> s = SegmentTree([1, 2, 3])
+        >>> s.right(1)
+        3
+        >>> s.right(2)
+        5
+        """
         return idx * 2 + 1
 
     def build(self, idx, l, r):  # noqa: E741
         if l == r:
-            self.st[idx] = A[l]
+            self.st[idx] = self.A[l]
         else:
             mid = (l + r) // 2
             self.build(self.left(idx), l, mid)
@@ -26,6 +45,15 @@ class SegmentTree:
             self.st[idx] = max(self.st[self.left(idx)], self.st[self.right(idx)])
 
     def update(self, a, b, val):
+        """
+        Update the values in the segment tree in the range [a,b] with the given value.
+
+        >>> s = SegmentTree([1, 2, 3, 4, 5])
+        >>> s.update(2, 4, 10)
+        True
+        >>> s.query(1, 5)
+        10
+        """
         return self.update_recursive(1, 0, self.N - 1, a - 1, b - 1, val)
 
     def update_recursive(self, idx, l, r, a, b, val):  # noqa: E741
@@ -44,6 +72,15 @@ class SegmentTree:
         return True
 
     def query(self, a, b):
+        """
+        Query the maximum value in the range [a,b].
+
+        >>> s = SegmentTree([1, 2, 3, 4, 5])
+        >>> s.query(1, 3)
+        3
+        >>> s.query(1, 5)
+        5
+        """
         return self.query_recursive(1, 0, self.N - 1, a - 1, b - 1)
 
     def query_recursive(self, idx, l, r, a, b):  # noqa: E741