How to create button to another stack

i want create button stack code

i have 2 stack.and stacks name "aa" , "bb"

i want create button in stack "bb" stack "aa" code

on createdigits   create button "test" of stack "bb" end createdigits

results: it's create in stack name "aa" , error message:

enter image description here

here's 1 way want:

on createdigits   set defaultstack "bb"   create button "test" end createdigits

GHI