Bez is dead on. The well light he mentioned are best, IMO, then there's the ones that are staked into the ground but that isn't going to cut it for ya. How aabout running the wires along the back wall and tie the lights onto the trunk of the tree to bring light up into the trees that way. It can be tie up in the back so the fixture isn't seen. Install a light every 6-8' would be best, IMO. I have never been a huge fan of very bright landscape lighting. Just enough to draw attention to a certain ares and bounce lights off it. Personally, I always install a bigger commercial, not those Home Depot Malibu cheap transformers to prevent voltage drop. Over the years, I have purchased a few light from these folks. Quality and well build, and not pay designer prices.
VOLTŪ LED Landscape Lighting | Outdoor Lights I believe you get trade discount.
2700 K bulb LED are best (MR16 Halogen are still my favorite), very similar to the old fashion halogen bulb color.
Jeff