Most references that help you to identify trees do so by the leaf and flowers or fruit. Some show the buds and the bark, especially for identifying them in winter. But when you know a tree, it takes only a glance to tell a sycamore from a weeping willow.
I found a reference that extends that skill: the Global Forest Science Trees of Canada Web site. Trees are divided into broad-leaved trees and conifers. It shows leaves and fruit but also tree silhouettes that teach the general shape of the tree.
At this point I’m trying to learn the difference between red spruce and white spruce. White spruce (above) has branches that are level at the top of the tree and droop near the bottom. Red spruce (left) has branches that reach up near the top and are level near the bottom.