I have essentially no insulation -- this is a cinderblock building -- and I don't have much in the way of tree cover directly over my unit, though I am a middle unit, so I at least have things better than the folks on edge units.
I don't know if any of these helps, but an ongoing project I'm doing is to get the house better insulated. For now, I did the following:
1) Installed cellular shades (the double-cell ones) in my bedroom and the kitchen. I'll probably eventually get them for all the windows. Windows are by far the largest source of heat leak or heat gain. We have double-pane windows installed in 1994. At best they're R3. The cellular shades double that. In the warmer weather I keep them down during the day to prevent solar heat gain.
2) Added cellulose insulation to the attic. We already did this around 1980, but I suspect it lost some of its effectiveness. Based on measuring ceiling temps compared to room temps in the winter, maybe the ceilings were around R9. I put 36 25-pound bags of insulation in the attic. It needed to be fluffed up. so I used a garbage pail and
concrete mixer. It took all told maybe 15 hours and $400 plus tax to install the insulation. Based on the depth, I'd say I went from R9 to around R40. It's already paying dividends. Today was 85°F. Normally the house would get into the high 80s at least without A/C on day like this. My bedroom stayed around 80. My mom's bedroom is maybe 77. Chalk up the difference to my body heat and the computer.
I'm thinking of putting 2" of polyisocyanate insulation on top of the outward facing interior walls when each room comes up for repainting. This would be a big job involving putting panels or sheetrock on top of the insulation. But it'll bring the exterior walls from around R6 up to about R20. If I can get vacuum insulation panels fairly cheap, those would be even better. A 1" thick panel is around R40, about 6 times the value of the best foam board per inch.
I also turned the boiler off back in March. The boiler makes heat and hot water but I figured I'm wasting at least 12 gallons a month of heating oil leaving it on when I don't need heat. I just turn it on about 15 minutes before I shower, then turn it off when I'm done. My only other use of hot water is to do dishes. For that I bought a 4 gallon water heater and put it under the kitchen sink. It uses about 30 kW-hr a month, costing about $10, compared to the extra 12+ gallons of oil costing at least $70 I'd waste just keeping the boiler warm. Besides that, the boiler is essentially a ~500W heat source right under my bedroom, which makes things hotter. Great in the winter, but a negative most of the other 9 months.
Anyway, look at what you can insulate given the bounds of your lease. You can at least get cellular shades to insulate the windows and keep out sunlight. As for the cinderblock walls, if your landlord is amenable maybe put 2" to 4" of polyisocyanate foam board covered by siding. It'll make the place look better outside, plus it'll get you to around R30. And see if you can get a better A/C. Look into the ones with inverters. We got one last year for the living room. Much quieter, plus it easily saved us 100 to 150 kW-hr/month.