Ask Mr. Smarty Plants

If we may address your last question first: 

Salix x sepulcralis is a hybrid of a Chinese species (Peking willow) and a European species (white willow), and is said to grow in Zones 5 to 8 in the United States. It is weak-wooded, fast-growing and, therefore, short-lived. It has aggressive roots, can lift sidewalks and interfere with sewer lines, often growing on soil surface, making a problem with mowing. It is susceptible to a number of pests and diseases, and notorious for littering the ground beneath it. That is to say, we don't like it.

The Lady Bird Johnson Wildflower Center will recommend only plants native not only to North America but to the area in which those plants are being grown. So, we will go to our Recommended Species section of our Native Plant Database, and look for trees native to the area of Middlesex County on the eastern side of Massachusetts, about 5 miles from Boston, in USDA Hardiness Zone 6a. 

You may follow the same steps we did, going to the Recommended Species section linked above, click on Massachusetts on the map (or the "MA" at the side, Massachusetts is a pretty small state to click). This will generate a list of 111 native plants for that state. On the sidebar on the right-hand side of that page, you can select "tree" under General Appearance, which is all we did as we did not know if you had a shaded situation, dry soil or what. Those are specifications you can put in when you are doing your own search. When we selected on "tree" and Narrow Your Search, we got a list of 43 trees native to Massachusetts. Of those, we chose 8 that we thought would work well for you, and will link you to the USDA Plant Profile map on each to make sure the trees we chose are native to Middlesex County. You will be able to follow each plant link to our webpage on the plant to learn what soils it likes, how much moisture it needs, when and what color it blooms, expected height, propagation and benefits.

Trees for Middlesex County, Massachusetts:

Chamaecyparis thyoides (Atlantic white cedar) - evergreen, 40 to 75 ft. high, habitat chiefly swamps and bogs, part shade, moist sandy soil USDA Plant Profile Map

Fagus grandifolia (American beech) - 50 to 80 ft., habitat wet lowland sites, part shade or shade USDA Plant Profile

Juniperus virginiana (Eastern red cedar) - 30 to 40 ft., evergreen, woodland edge, savannahs USDA Plant Profile

Larix laricina (Tamarack) - 50 to 75 ft., cold bogs and wet forests, sun or shade USDA Plant Profile

Liriodendron tulipifera (Tuliptree) - up to 150 ft. tall, low, rich woods, stream banks, sun or shade, USDA Plant Profile

Magnolia acuminata (Cucumbertree) - 60 to 75 ft. tall, low rich woods, stream banks, sun part shade or shade USDA Plant Profile

Pinus strobus (Eastern white pine) - 75 to 100 ft. tall, evergreen, rocky stream banks, sun, part shade or shade USDA Plant Profile

Quercus palustris (Pin oak) - 60 to 70 ft., wet woods, bottomlands, sun, part shade or shade USDA Plant Profile

From our Native Plant Image Gallery:

Chamaecyparis thyoides

Fagus grandifolia

Juniperus virginiana

Larix laricina

Liriodendron tulipifera

Magnolia acuminata

Pinus strobus

Quercus palustris