$scope.tree = Tree.parentize({
    title: 'root',
    children: [{
        title: 'child one',
        children: [{
            title: 'leaf one',
            children: []
        }, {
            title: 'leaf two',
            children: []
        }, {
            title: 'leaf three',
            children: []
        }]
    }, {
        title: 'child two',
        children: [{
            title: 'leaf four',
            children: []
        }, {
            title: 'leaf five',
            children: []
        }]
    }]
});

'use strict';

var Tree = (function () {
    var parentize = function(tree) {

        angular.forEach(tree.children, function(value, key) {
            this.children[key].parent = function() {
                return tree;
            };
            parentize(value);
        }, tree);
        return tree;
    };

    return {
        parentize: parentize
    };
})();