Ruby on rails 在rails项目中显示dropdownlist

我的rails项目中有这个常量

   ID_METHODS = {      
          :category => [
              "name 1",
              "name 2",
              "name 3"
              "name 4",
              "name 5",
              "name 6"
              "name 7",
              "name 8",
              "name 9"
          ]
      }

并使用以下代码在dropdownlist中显示它们

<%= f.select :id_methods, CategoryConstants::ID_METHODS[:staff].collect { |i| [i, i] }, {include_blank: "Select"} -%>

但我需要在dropdownlist中输出，如下所示

name 1
 name 2
 name 3
  name 4
  name 5
name 6
name 7 
 name 8
 name 9

---

我怎样才能做到这一点？

我想您需要

分组选项来选择

前

然后



请详细说明
选择子类别的分组选项仅显示两个级别，但我需要在4个级别中显示它们
name 1
 name 2
 name 3
  name 4
  name 5
name 6
name 7 
 name 8
 name 9

 collection = ["North America",[["United States","US"],["Canada","CA"]]]

<%= select_tag(::id_methods, grouped_options_for_select(collection, selected_key = " ", prompt = nil)) %>