code: def priv_insert(s, value)
        if s.empty?
          if @data.nil?
            @data = [value]
          else
            @data.push value
          end
        else
          index = key(s.first)
          subtree = if @children[index]
                      @children[index]
                    else
                      @children[index] = PlTrie.new
                    end
  
          subtree.priv_insert(s[1..-1], value)
        end
      end
docs: private