Returns leaf nodes from a tree where the elements return true for a given predicate

CollectLeaves.fsx

type 'a Node = Group of 'a Node list | Leaf of 'a

let tree = Group [ Group [Leaf 1; Leaf 2; Leaf 3]; Group [Leaf 6]; Leaf 9; Leaf 10 ]
let isEven n = n % 2 = 0

let flip f a b = f b a
let (>>=) = flip List.collect

let rec collectLeavesBy predicate = function
  | Group xs -> xs >>= (collectLeavesBy predicate)
  | Leaf x -> if predicate x then [Leaf x] else []

collectLeavesBy isEven tree |> printfn "%A"