docs: def get_leaf(self, index):
          """
          Returns a leaf at the given index.
          :param index:
          :return: leaf (value) at index
          """
          leaf_level_index = len(self.tree['levels']) - 1
          if index < 0 or index > len(self.tree['levels'][leaf_level_index]) - 1:
              # index is out of bounds
              return None
          return self.tree['levels'][leaf_level_index][index]