The Chipmunk and Acorns (fr Mr CCL)

Alvin, the chipmunk, is at the foot of a Supertree (See Point A).  There are some acorns at the top of the Supertree (See Point B).  How many ways are there for the chipmunk at Point A to reach the acorns at Point B?
Note: The chipmunk can only climb upwards and not downwards.