Tree Algo

tree_algo.rb

sections = Section.includes(:questions).as_json(
  only: [:_id, :id, :name, :description, :template_id, :section_id],
  include: {
    questions: {
      only: [:_id, :description, :helptext]
    }
  }
)
section_hash = sections.index_by { |node| node['_id'].to_s }

section_hash.each_value do |node|
  section_id = node['section_id'].to_s
  next if section_id.blank?
  children = section_hash[section_id]['sections'] ||= []
  children << node
end

result = []
section_hash.each_value do |value|
  result.push(value) if value['template_id'].present?
end