example suggestion: tree with a variable number of children

Starting point:

NodeID : U64

Node : { value: Str, children :  List NodeID}

tree : Dict NodeID Node
tree = Dict.empty {}
       |> Dict.insert 0 { value: "hey", children: [1]}
       |> Dict.insert 1 { value: "hey!", children: []}

Brendan also suggested a type like this, which could look nicer/simpler:

Node: [Element { branch: List Node, ...}]

We may want to make a simple example and one optimized for performance but we can worry about that later.

Start with the NodeID, Node, and tree examples in the issue, then compare the proposed variable-child representations. Clarify whether the goal is a simple example, a performance-oriented example, or both; done requires an agreed example scope and representation.