input: def insertion_sort(arr):
      """Sort the list of n distinct integers using the insertion sort algorithm.
      >>> insertion_sort([5, 2, 9, 1, 5, 6])
      [1, 2, 5, 5, 6, 9]
      >>> insertion_sort([10, 7, 8, 9, 1, 5])
      [1, 5, 7, 8, 9, 10]
      """
      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
output:     return arr