Oh, I oh I don't know. My romantic side was getting carried away I suppose.
Direct sunlight would be harmful for people too, so they would filter out that anyway. The environment under these windows would always
be regulated, and the stars would just be a view that wouldn't contribute much radiation and any heat to the ship's environment under any circumstances (only enough visible radiation to see things would be allowed through, and no other wavelengths).
Of course, the arboretum wouldn't need the window for the sake of the trees; why would you assume that I would think it would? The window would only be for the benefit of the people in the first place. In addition, the arboretum on the TMP Enterprise did have side facing windows to space. I was extrapolating from that I suppose.
But the artificial sunlight in an arboretum would waste the view to space at least half the time. Like I said, I suppose I was just getting carried away with the idea of a walk in nature under real stars.