code: function pathToNode(id) {
    if (!id) {
      return Immutable.Set();
    }
  
    // Recurse from child to parent by cutting off the last two characters, treating the shortened
    // string as a parent pointer.
    return id.length > 0 ? Immutable.Set([id]).union(pathToNode(id.slice(0, -2))) : [];
  }
docs: Returns an Immutable.Set of node ids. The ids are the path from root to that id. For example,
  given the id '0.0.0', this function will return ['0', '0.0', '0.0.0'].
  
  @param {string} id - the node id to get the path from the root node to.
  @returns {Immutable.Set}