Render tree within a single sql query

gistfile1.rb

  def render_tree(nodes = [])
    stack = []
    html = ""
    nodes.each do |node|
      if stack.empty?
        html << start_tag(node)
        stack.push(node)
        next
      end
      if stack.last.lft < node.lft && node.lft < stack.last.rgt
        if node.leaf?
          html << node_tag(node)
        else
          html << start_tag(node)
          stack.push(node)
        end
        if node.rgt + 1 == stack.last.rgt
          html << end_tag
          stack.pop
        end
      else
        html << end_tag
        stack.pop
        redo
      end
    end
    content_tag(:ul, html.html_safe, :id => "category-tree")
  end