input: Write a python function to find the shortest unique substrings in a given input string.
  assert find_shortest_unique_substrings("banana") == ["b", "a", "n", "an", "ba", "na", "ban", "nan", "ana", "nana", "bana", "banan", "banana"]
  assert find_shortest_unique_substrings("abc") == ["a", "b", "c", "ab", "bc", "abc"]
  assert find_shortest_unique_substrings("aabb") == ["a", "b", "aa", "ab", "bb", "aab", "abb", "aabb"]
output: def find_shortest_unique_substrings(s):
      unique_substrings = set()
      
      for length in range(1, len(s) + 1):
          for start in range(len(s) - length + 1):
              unique_substrings.add(s[start:start + length])
      
      return sorted(unique_substrings, key=lambda x: (len(x), x))