Javascript Algorithm to build an org chart from an array of related objects

RelationshipTree.js

var ary = [
    {id: "a", parent: 0},
    {id: "b", parent: "a"},
    {id: "c", parent: "b"},
    {id: "d", parent: "c"},
    {id: "e", parent: "d"},
    {id: "f", parent: "e"},
    {id: "g", parent: "f"},
    {id: "h", parent: "g"},
    {id: "i", parent: "h"},
        
    {id: "1", parent: "Dan Band"},
    {id: "2", parent: "1"},
    {id: "3", parent: "2"},
    {id: "4", parent: "3"},
    {id: "5", parent: "4"},
    {id: "6", parent: "5"},
    {id: "7", parent: "6"},
    {id: "8", parent: "7"},
    {id: "9", parent: "8"},
            
    {id: "c1", parent: "c"},
    {id: "c2", parent: "c1"},
    {id: "c3", parent: "c2"},
    {id: "c4", parent: "c3"},
    {id: "c5", parent: "c4"},
    {id: "c6", parent: "c5"},
    {id: "c7", parent: "c6"},
    {id: "c8", parent: "c7"},
    {id: "c9", parent: "c8"}
      
];

var monkey = {
    // The Tree
    "tree": {
        "children": []
    },

    // Main function to build the tree
    "build_tree": function (ary, id_field, parent_field) {
        this.tree[id_field] = "root";
        this._build(ary, id_field, parent_field);
        return true;
    },

    // Function to push children in arrays
    "_build": function (ary, id_field, parent_field) {
        var x,
            i;

        this.map = {};

        // Step 1. Create a "hash map" of all objects
        for (i = 0; i < ary.length; i++) {
            this.map[ary[i][id_field]] = ary[i];
        }

        // Step 2. Iterate over the "hash map"
        for (x in this.map) {
            // 2a. Does the current object have a parent on the map?
            if (this.map[this.map[x][parent_field]]) {
                // This object has a parent. Hop in their kiddie pool (children array)!
                if (this.map[this.map[x][parent_field]].children) {
                    this.map[this.map[x][parent_field]].children.push(this.map[x]);
                } else {
                    this.map[this.map[x][parent_field]].children = [this.map[x]];
                }
            } else {
                // Object has no parent. It's a Node. Add to root's children.
                this.tree.children.push(this.map[x]);
            }
        }
    },

    // Find a node by id in the map, and apply a function to it,
    // and all of its ancestors
    "_back_trace": function (id, parent_field, fx) {
        if (this.map[this.map[id][parent_field]]) {
            // Apply the function
            fx(this.map[id]);
            this._back_trace(this.map[id][parent_field], parent_field, fx);
        }
    }
};

monkey.build_tree(ary, "id", "parent");
console.log(JSON.stringify(monkey.tree));