Add/Insert New Value into OPTIONSET

hi all

I have created a optionset with 1 value in it, but on runtime when the user press button
i would like to add another two values in it, i can add the values and they display in the
optionset list but when i click on any newly added value it doesn't get selected and won't show

i have tried many different ways doing it but can't get it work.

can anyone help me with this please.

thanks