VEHICLES = Choices(
    ("RedCar", "Red car"),
    ("GreenCar", "Green car"),
    ("RedTruck", "Red truck"),
    default="RedCar",
    groups={
        "red": ["RedCar", "RedTruck],
        "cars": ["RedCar", "GreenCar"],
    },
)

class Foo(models.Model):
    vehicle = ChoiceCharModelField(VEHICLES, verbose_name="Vehicle")
    vehicles = ChoiceArrayModelField(ChoiceCharModelField(VEHICLES), verbose_name="Vehicles")

# In template:
# {{ foo|"vehicle" }}