Trees are hand-placed in logical locations for 5 holds - Whiterun, Markarth, Riften, Solitude, and Windhelm.
Trees in Cities - The Complete Pack aims to do just that, and it accomplishes its goal exceedingly well. There are mods that add more people, or new buildings, but there are few that add flora and plantlife to the cities. And while some of this apparent lack of life is understandable for certain cities, major hold capitols such as Solitude, Markarth or Whiterun should be teeming with life. Skyrim is a beautiful game, to be sure, but it's cities are somewhat less interesting.
