如何创建一个多选嵌套下拉菜单？

Question

我想使用Angular创建一个多选嵌套下拉菜单。与此类似：

https://codepen.io/sathomas/pen/VpJeEo（请参见“搜索多个”示例）

html：

<nested-select options="vm.populations" placeholder="Search items" label="Permanently Open"
    multiple collapsible fixed-menu allow-select-all></nested-select>

控制器：

angular.module('myApp', ['ngSanitize','ngMaterial', 'ngMdIcons'])

.controller('myCtrl', [function myCtrl () {
    var vm = this;

    // static collection for test/demo
    vm.populations = [
        { text: "Item 1" }, 
        { text: "Item 2",
            children: [
                { text: "Item 2.1" }
            ]
        }, 
        { text: "Item 3",
            children: [
                { text: "Item 3.1",
                    children: [
                        { text: "Item 3.1.1",
                            children: [
                                { text: "Yet Another Item 3.1.1.1" }
                            ]
                        },
                        { text: "Item 3.1.2" }
                    ]
                }, 
                { text: "Item 3.2",
                    children: [
                        { text: "Item 3.2.1" },
                        { text: "Item 3.2.2" }
                    ]
                },
                { text: "Item 3.3" }
            ]
        }
    ];
}])

但是上面的代码是使用angularJs完成的。是否有Angular实现来做到这一点？我看过材质库，但是没有示例包含嵌套的多个可选项目。 https://material.angular.io/components/select/examples