I think this is basswood, also known as linden. The reason I think that is because that's what I remember this tree being at other times of the year. (This is a tree at Sage, near the corner of a building.)
When I look up picture of linden or basswood buds, this is not what I see. However, this is a bud opening up, which is different. The pictures show closed reddish buds. I should continue to watch this tree, to see if I continue to think it's basswood.