gistfile1.txt

<div class="nested-categories nested-group">
    <%= f.semantic_fields_for :trade_categories, builder: Formtastic::FormBuilder do |trade_categories| %>
        <%= render 'trade_categories/trade_category_fields', trade_categories: trade_categories %>
    <% end %>
</div>

trade_category_fields.html.erb

<div class="nested-category">
    <%= render 'shared/nested_semantic_errors', f: trade_categories %>
    <%= trade_categories.input :trade_category_type, label: false, input_html: { class: 'form-control', placeholder: t('trade_category_type') }, wrapper_html: { class: 'category-name' }  %>
    <div class="nested-options">
        <%= trade_categories.semantic_fields_for :trade_options, builder: Formtastic::FormBuilder do |trade_options| %>
            <ul>
                <%= render 'trade_categories/trade_option_fields', trade_options: trade_options %>
            </ul>
        <% end %>
    </div>
    <div class="clearfix">
        <%= link_to_add_association t('add_option'), trade_categories, :trade_options, class: 'btn btn-primary pull-right add-option' %>
        <%= link_to_remove_association t('remove_category'), trade_categories, class: 'btn btn-danger', wrapper_class: 'nested-category' %>
    </div>
</div>

trade_category_type.rb

class TradeCategoryType < ApplicationRecord
  include Accountable

  has_many :trade_categories, dependent: :restrict_with_exception
  has_many :crew_trade_categories, dependent: :restrict_with_exception
  has_many :subcontractor_crews, through: :crew_trade_categories

  scope :collection, (-> { all.collect { |sub| [sub.name, sub.id] } })
end

trade_option.rb

class TradeOption < ApplicationRecord
  include Accountable

  default_scope { order(name: :asc) }

  validates :name, presence: true

  belongs_to :trade_category, touch: true
  has_many :trade_data, as: :trade_data_parent
end