A study of houses in Portland, Oregon found that on average, street trees add 3% to sales price and reduce time-on-market (TOM) by 1.7 days. In addition, the study found that the benefits of street trees spill over to neighboring houses.
Donovan, Geoffrey H., and David T. Butry. (2010). Trees in the city: Valuing street trees in Portland, Oregon. Landscape and Urban Planning, 94(2), 77-83.