Learn Spanish (Latin America): El pájaro y el árbol se traen un beneficio el uno al otro. - The bird and the tree bring a benefit to each other.

The pronoun se can be reciprocal ('each other') or reflexive ('themselves'). Without the extra clarification, se traen un beneficio could technically mean 'they bring a benefit to themselves.' Adding el uno al otro completely removes this ambiguity and strongly emphasizes that the bird and tree help each other.

Why is it el uno al otro in the singular instead of plural los unos a los otros?

We use the singular forms el uno and el otro when exactly two individuals are interacting. Since there is just one bird and one tree, it is literally 'the one to the other.' You would only use the plural los unos a los otros if there were multiple birds and multiple trees involved.

Why are we using the masculine form el uno and el otro?

The phrase has to match the grammatical gender of the subjects. Both el pájaro (the bird) and el árbol (the tree) are masculine words, so we use the masculine uno and otro. If we were talking about two feminine nouns, like a bee (la abeja) and a flower (la flor), it would change to la una a la otra.

Where does the al in el uno al otro come from?