tryingout: All possible subsets of set with duplicates removed

Given a set of character {a, b, c, d} find all subsets. The final list should not have any duplicate entry.

   1:  /// <summary>

   2:  /// Given set {a, b, c, d} below are all subsets

   3:  ///     d

   4:  ///     dc     c

   5:  ///     dca    cb     b   a

   6:  ///     dcba   cba    ba

   7:  ///     dca    ca

   8:  ///     db

   9:  ///     dba

  10:  ///     da

  11:  ///  This algortithm picks an item from input set and prepends it with items present in output set as well as adds the item

  12:  ///  This guarantees unordered combinations. i.e. it treats "ab" and "ba" same ways.

  13:  /// </summary>

  14:  /// <param name="data"></param>

  15:  /// <returns></returns>

  16:  static List<string> GetAllSubsets(char[] data)

  17:  {

  18:      List<string> result = new List<string>();

  19:      for (int i = 0; i < data.Length; i++)

  20:      {

  21:          for (int j = result.Count - 1; j >= 0; j--)

  22:          {

  23:              StringBuilder sb = new StringBuilder(result[j]);

  24:              sb.Insert(0, data[i]);

  25:              result.Add(sb.ToString());

  26:          }

  27:          result.Add(new string(new char[] { data[i] }));

  28:      }

29:

  30:      return result;

  31:  }

tryingout