Sometimes some Buddhists find it convenient to think of the community of Buddhists as a whole as a kind of concrete symbol of the much more abstract notion of the Noble Sangha of excellent people to which they go for refuge. These three roots support the trunk of the tree, which is the single act of going for refuge, the essence of Buddhism as an organized religion. There are many different ways of going for refuge. Ultimately, you could say that there are as many ways as there have been individual Buddhists throught the history of Buddhism, because ultimately going for refuge is an individual decision that each individual has to figure out how to put into practice is his or her life. We can think of the individual Buddhists as the leaves on the tree.
Leaves grow on twigs attached to limbs that grow out of branches out of the main trunk.
So now let's look at the main branches. These people chose to base their practice on doctrines that were believed by everyone to be the public teachings of the Buddha to his monks and lay disciples. At one time there were many limbs of this Savaka branch, but only one of them has lived to modern times. That is the limb known as Theravada , which means the teachings of the elders. An elder is a monk who has been ordained for a minimum of ten years and who is acknowledged to have attained insight.