I have been brushing docks for over 40 years and have tried every possible combination of cover. PVC, milk bottle trees, xmas trees, willow, cedar trees, sunk to the bottom, suspended whatever is possible I tried. Best results came using fresh 6'-8' cedar trees suspended on ropes with the tops about 5' below the surface.
I added some fresh trees to our slips last week and the fishing picked up immediately.
Xmas trees take too much weight to sink and hang more lures. Willow works well but the beavers cut the ropes and steal it as fast as you hang it. PVC will work somewhat but if any other slips near by are baited with real trees will attract most of the fish.
Good luck with whatever you try.