Yes, planting trees (in the spring or fall-too hot to plant now) is a good idea
BUT
It also depends on where you live, and what are the water restrictions.
Several years ago, I had over 300 trees in my yard, but because of the drought
and horrible insects for the past few years (I refuse to use chemicals),
I've lost 35-40% of my trees.
Plant to your area, and plant with low water use in mind.
Regarding the original intent of this thread-
Insulate, insulate, insulate.
Again, it's too hot to get into an attic now, but come fall, add to it. Check the vapor barrier also.
Many utility companies will give you a "door test", if not check into a reputable outfit to have it done. My house was leaking like a sieve when they did mine.
Nooks and crannies are the culprit. Pipes coming into the house, electrical outlets, windows/doors, all those vents on your roof; any opening will exchange air.
I was lucky enough to qualify for the energy efficient program pushed through
by Obama, and they pumped in 35 bales of recycled newspapers into the walls, attic.
They put up batts on my basement ceiling, gave me new energy efficient windows/doors, new frig/stove.
I know that people in higher income brackets don't qualify, and it's hard to buy a new frig,
but insulation is inexpensive and can be done by most homeowners themselves.
Caulking too.
Even a diy'er can use the blown in cellulose themselves. The payback is almost immediate.
My light/gas bills now average 30E-13G, before gas was 120-140 in the winter, lights were 50-60 every month.And the old stand-by, power strip everything electrical
(except the frig) and turn the switch off when you leave or go to bed.
Rain-barrels if your lucky enough to have rain.