Adding a dropdown to a button in C#

You could create a custom control based on the button control and add additional propereties and override the button OnClick event

One of the properties could be the list of options you talk about and a ListBox to take the options, then when the button is clicked a list box shows bellow the button to expose the options, your button control would also have the ListBox OnClick event where you would do your processing.

Does this make sense?

I don't want to use dropdown list.

i just want to use button with additional options

I think u can implement such by setting an event handler to the OnSelectedIndexChanged property of  the dropdown list.