The Smooth Alder Tree (Alnus serrulata 'Smooth') also known as the Tag Alder Tree is a 

s a multi-stemmed, suckering, thicket-forming, large deciduous shrub or small tree that t is most often seen in a multi-trunked form with a densely branched crown. The trunks feature smooth gray bark, with flowers appearing in separate catkins in March-early April before the leaves emerge. Male catkins (brownish-yellow flowers) are slender, cylindrical and droop in clusters of 2-5 from near the branch tips to 2-4" long. Female catkins (bright red flowers) are upright cylinders (to 1/4" long) located at the twig tips in clusters of 2-5. Female flowers are pollinated by wind. Female catkins develop into 1-inch long fruiting cones (strobiles) to 3/4” long containing winged nutlets (seeds). Fruiting cones mature to dark brown in fall, with persistence into winter. Cones have woody scales and resemble small pine cones.

Prefers full sun to partial shade, grows in medium to wet soils, will tolerate mucky soils. Avoid full shade. Winter hardy

What you are purchasing is 1 Smooth Alder tree, a size of your choosing. Handle with care.