Is a tree a decomposer or a producer or consumer?

Answer 1

A tree is both a consumer and a producer. It consumes water, nutrients from the soil, and carbon dioxide from the air while producing tree mass (leaves, bark, wood).

Generally though, it is considered a producer.

Note that despite the "expert answer" trees do not make energy from light - they convert light energy into chemical energy. By the first law of thermodynamics you cannot "make energy" you can only convert it from one form to another.