This is hurting my brain! I want to recurse over a tree structure and collect all instances that match some filter into one list. Here's a sample tree structure type Tree = | Node of int * Tree list Here's a test sample tree: let test = Node((1, [Node(2, [Node(3,[]); Node(3,[])]); Node(3,[])])) Collecting and filtering over nodes with and int value of 3 should give you output like this: [Node(3,[]);Node(3,[]);Node(3,[])]