tree:

keys([tree])

Returns an array of the top-level keys in the indicated tree.

$ cat letters.yaml
a: The letter A
b: The letter B
c: The letter C
$ ori keys letters.yaml
- a
- b
- c
g a The letter A ->a a b The letter B ->b b c The letter C ->c c
g 0 a ->0 0 1 b ->1 1 2 c ->2 2
Input tree
Keys as an array

See also values.