input: Write a function to sort a list of n distinct integers using the insertion sort algorithm. The function should take a list of integers as input and return the sorted list.
  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
      return arr
  
  assert insertion_sort([5, 3, 8, 6, 2])==[2, 3, 5, 6, 8]
  assert insertion_sort([9, 1, 3, 5, 7])==[1, 3, 5, 7, 9]
  assert insertion_sort([1, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
  assert insertion_sort([5, 4, 3, 2, 1])==[1, 2, 3, 4, 5]
  assert insertion_sort([])==[]
output: 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
      return arr