docstr: Returns sum of arr[0..index]. This function assumes that the array is preprocessed and partial sums of array elements are stored in bit_tree[]. 
docstr_tok: ["Returns","sum","of","arr","[","0","..","index","]",".","This","function","assumes","that","the","array","is","preprocessed","and","partial","sums","of","array","elements","are","stored","in","bit_tree","[","]","."]
code: def get_sum(self, bit_tree, i):
      """
      Returns sum of arr[0..index]. This function assumes that the array is preprocessed and partial sums of array elements are stored in bit_tree[].
      """
  
      s = 0
  
      # index in bit_tree[] is 1 more than the index in arr[]
      i = i + 1
  
      # Traverse ancestors of bit_tree[index]
      while i > 0:
          # Add current element of bit_tree to sum
          s += bit_tree[i]
  
          # Move index to parent node in getSum View
          i -= i & (-i)
      return s
  
label_desc: Use image node_id 2 for calling the Fenwick_Tree obj's underlying member method code with example usage: obj.get_sum(bit_tree, i) and returns: s