“The Sibley Guide to Birds,” published in 2000, broke new ground with its comprehensive illustrations of North American birds in all of their phases – male and female, adult and juvenile, in breeding and non-breeding plumage. This hefty volume, since supplemented with more portable Eastern and Western editions, has sold more than a million copies. Now Sibley has shifted his gaze slightly to take in another ubiquitous feature of our landscapes, wild and domestic: trees. “The Sibley Guide to Trees” released Tuesday, aims to be “a tree guide for bird-watchers,” Sibley says.