I like to dress in "civilian clothes", i.e. in clothes that are good for day to day life once I'm off the bike. So that usually means dress trousers and either a nice sweater or a suit, except in summer when I often wear a short-sleeve shirt.
From late fall to early spring, I usually wear long underwear under my trousers. Very effective, as thermal underwear usually keeps me warm down to -10 C to -25 C, depending on wind and length of the ride. At -10 C, I can ride all day. At -25 C, I'm OK for 1 hour; if the ride is longer, I also wear my rain trousers, which are good at cutting the wind.
Regards,