QUERCUS - An oak is a tree or shrub in the GENUS Quercus of the beech family Fagaceae, having approximately 600 SPECIES.

As BONSAI>BONSAI>BONSAI commonly used in Europe are -

Quercus Rober - English oak (or French oak)

Quercus Suber - Cork BARK oak

A full list of Quercus species is available on the web link above