input: def insertion_sort(arr):
      """
      This function sorts a list of distinct integers using the insertion sort algorithm.
      
      >>> insertion_sort([64, 34, 25, 12, 22, 11, 90])
      [11, 12, 22, 25, 34, 64, 90]
      >>> insertion_sort([7, 5, 3, 9, 6])
      [3, 5, 6, 7, 9]
      >>> insertion_sort([1, 2, 3, 4, 5])
      [1, 2, 3, 4, 5]
      """
      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