[[xy, ["Name 3", ["SubName 1", "SubName 2"]],
      ["Name 1", ["NameSub 1", "NameSub 2"]], ...],
 [yz, ["Name 10", ["SubNamex 1", "SubNamex 2"]],
      ["Name 6", ["NameSubx 1", "NameSubx 2"]], ...]]

[[xy, ["Name 1", ["NameSub 1", "NameSub 2"]],
      ["Name 3", ["SubName 1", "SubName 2"]], ...],
 [yz, ["Name 6", ["NameSubx 1", "NameSubx 2"]],
      ["Name 10", ["SubNamex 1", "SubNamex 2"]], ...]]

mylist.sort(key=lambda x: x[1])

mylist.sort(key=itemgetter(2,1))