def create_entity(self, name, gl_structure, description=None):
new_entity = Entity(name, gl_structure, description=description)<EOL>self.entities.append(new_entity)<EOL>return new_entity<EOL>
Create an entity and add it to the model.

:param name: The entity name.
:param gl_structure: The entity's general ledger structure.
:param description: The entity description.

:returns: The created entity.