input: from typing import List
  
  def insertion_sort(list: List[int]) -> List[int]:
      """ Implements an insertion sort algorithm.
      >>> insertion_sort([3, 1, 4, 1, 5, 9, 2, 6, 5])
      [1, 1, 2, 3, 4, 5, 5, 6, 9]
      >>> insertion_sort([])
      []
      >>> insertion_sort([1])
      [1]
      >>> insertion_sort([2, 1])
      [1, 2]
      """
output:     for i in range(1, len(list)):
          key = list[i]
          j = i - 1
          while j >= 0 and key < list[j]:
              list[j + 1] = list[j]
              j -= 1
          list[j + 1] = key
      return list