input: def insertion_sort(arr):
      for i in range(1, len(arr)): 
          key = arr[i] 
          j = i-1
          while j >= 0 and key < arr[j]: 
                  arr[j + 1] = arr[j] 
                  j -= 1
          arr[j + 1] = key
  
  # Example usage:
  # >>> insertion_sort([3, 1, 4, 1, 5, 9, 2, 6])
  # [1, 1, 2, 3, 4, 5, 6, 9]
  # >>> insertion_sort([10, 8, 3, 5, 2, 7, 1, 4])
  # [1, 2, 3, 4, 5, 7, 8, 10]
output:     return arr