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
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
private