  In this note, we introduce monoidal subcategories of the tensor category of
finite-dimensional representations of a simply-laced quantum affine algebra,
parametrized by arbitrary Dynkin quivers. For linearly oriented quivers of
types A and D, we show that these categories provide monoidal categorifications
of cluster algebras of the same type. The proof is purely
representation-theoretical, in the spirit of [arXiv:0903.1452].
