Which Tolkien short story features a painter who creates a vast tree and a landscape?

The Tolkien short story featuring a painter who creates a vast tree and landscape is Leaf by Niggle.

Niggle is an artist whose attention to individual leaves gradually expands into a vision of an entire tree and surrounding country. The story explores artistic creation, duty, distraction, mortality, and the relationship between a small piece of work and a much larger imagined reality.

Tolkien wrote the story during the Second World War, and it was first published in 1945 in the Dublin Review. It is frequently read as a partly autobiographical reflection on Tolkien’s own experience of building immense fictional histories while managing academic responsibilities and everyday obligations.