Thomas: Thanks for the kind words, and, yes, you're always welcome to re-use my pictures. As for your architecture question, I thought about it quite a bit during my late-February round at Harbour Town, which features numbers trees in/adjacent to bunkers (to say nothing of the many tree-dotted waste areas lining fairways, there are trees in bunkers behind 7 green and to the right of 16 green--both pictured below). Implicit in your question is that it is limited to green-side bunkers, or those that have the potential to catch approach shots (or tee shots on par 3s). Obviously, there are many off-the-tee hazards that are doubly penal--rough, pine straw, or "other" with trees all around. So the question is really whether we should accept the same possibility in by-the-green hazards or whether those should be "cleaner" and less penal. Although I'm generally an opponent of internal inconsistencies in most things, I'm inclined to say that it's okay in this instance--the reason being that recovery opportunities dwindle as you get closer to the green. Accordingly, to the extent there are trees in/adjacent to greenside bunkers, the bunkers must be amply large and the trees must be sufficiently narrow to allow the golfer to play around them.
Harbour Town GL, Hole 7 (reverse view from behind green)
Harbour Town GL, Hole 16 (reverse view from back right of green)