In this model, a small plant grows attached to the bark of a large tree and gains a better position for catching light. The scenario states that the tree is neither helped nor harmed. What is this interaction called?

Explication

One species gains while the other is stated to be unaffected, which matches commensalism exactly. A relationship in which the second species is gradually harmed does not fit, because this scenario states that the tree is neither helped nor harmed.