The Tree of Enlightenment is a very ambitious work in that in the space of less than 400 pages attempts to summarize and serve as guide to 2,500 years of Buddhist practices, writings, philosophies, symbolisms, etc.
This work is a remarkable accomplishment in that a beginning reader can, in fact, learn a substantial amount about Buddhism(s) and its development, and the many cultures that it penetrated, without having one’s head reel from an overload of minute facts. The clear and logical organization, that goes from introducing the fundamentals, to some elaboration in considering the Mahayana tradition, to a concise but credible introduction to Vajrayana (commonly know as Tibetan Buddhism), and finally, a succinct discussion of the foundation of all Buddhist philosophical discourse–the Abidharma.
The language in the book is easily accessible and the book may be downloaded for free, or acquired for no cost from the Buddha Educational Foundation. Its one downfall is being rather poorly written and therefore this reader would recommend the significantly better written A Concise History of Buddhism by Andrew Skilton’s; if the pocketbook allows that.