Build another tuple-of-tuples out of another_choice, then concatenate:
final_choices = (another_choice,) + my_choices
Alternately, consider making my_choices a list-of-tuples instead of a tuple-of-tuples by using square brackets instead of parenthesis:
my_choices=[
('1','first choice'),
('2','second choice'),
('3','third choice')
]
Then you could simply do:
my_choices.insert(0, another_choice)