Simple tree implementation in TypeScript using only a single one-line function. It's obviously seriously basic and insert/delete operations would not be very efficient but then again your data is immutable so who needs to do that right? ;)

simple_tree.ts

function N(...nodes:any[]) {
    return nodes;
}

var tree =
    N("root",
        N("one", "one",
            N("two", "two")),
        N("one", "one",
            N("two")));

// Get a Node by index
tree[1][1] // -> "one"

// If a node has children they are at index + 1
tree[1][2] // -> ["two", "two"]

// To get the parent of a node, knock off an index and -1 it
tree[0] // -> "root"