Laravel 5 recursive query

使用 laravel 5 做的例子， 以下幾個站說明的很清楚

https://itsolutionstuff.com/post/laravel-5-category-treeview-hierarchical-structure-example-with-demoexample.html

https://heera.it/laravel-model-relationship

https://heera.it/laravel-nested-relationship-revised#.V9ntypN94dU