The answer would depend on why you feel a need for window treatment on such a lovely window. You might want to consider a curtain wall, floor to ceiling, falling in front of the window seat. This treatment would not obstruct the architecture of the round window when the curtain is fully open and pulled to the sides. When closed it would make the dining area more intimate. Two recommendations if you consider this approach. 1. Use a thin, light weight fabric so it doesn't "bunch" when open. 2. Consider a subtle organic pattern to balance your geometric theme (I'd recommend Galbraith & Paul). Best, Angela.

I would probably hang the drapery across the entire window if you want to avoid doing any custom treatment.

Thank you for your comments :)
I could use some window treatment because the neighbor house is facing this room..it is far, but during the dark is still pretty visible...