Short answers, pulled from the story.
Tree and Leaf is a small anthology by J. R. R. Tolkien published in 1964, originally illustrated by Pauline Baynes. It collected a revised version of his essay "On Fairy-Stories" and his allegorical short story "Leaf by Niggle".
"On Fairy-Stories" was originally published in 1947 in a volume called Essays Presented to Charles Williams. It was later revised and included in Tree and Leaf in 1964.
"Leaf by Niggle" was first published in the Dublin Review in 1945. It later appeared in the 1964 anthology Tree and Leaf and was re-issued in The Tolkien Reader in 1966.
Tolkien's poem "Mythopoeia" was added to the second edition in 1988. His poem "The Homecoming of Beorhtnoth Beorhthelm's Son" was added to the third edition in 2001.
The original 1964 edition of Tree and Leaf was illustrated by Pauline Baynes.
Both "On Fairy-Stories" and "Leaf by Niggle" were re-issued in The Tolkien Reader, published in 1966. Both pieces have also appeared in various other subsequent collections.