Trees

The origin of the name dendrite from the good people at Scholarpedia -

The receiving or input pole [of the neuron] generally consists of extensively branching tree-like extensions of the soma membrane known as dendrites (coined in 1889 by William His from dendros (Greek) meaning tree) which arises in vertebrate neurons directly from the cell body (the body is also a receiving site in most neurons).

This stuff is probably taught on day one in school. Self-teaching is a truly haphazard path.