generic xsl to transfrom xml to html

Here is the xml files format:
 <Root>
    <a1>value-of-a1</a1>
    <a2>value-of-a2</a2>
    <a3>
        <a3i>value-ofa3i</a3i>
        <a3ii>
              <a3iia>value-ofa3iia<a3iia>
              <a3iib>value-ofa3iib<a3iib>
    </a3>
    <a4>value-ofa4</a4>
  ..
 <Root>

The result I'm expected is like this:
 a1                    value-of-a1
 a2                    value-of-a2
 a3 - a3i              value-of-a3i
 a3 - a3ii - a3iia     value-of-a3iia
 a3 - a3ii - a3iib     value-of-a3iib
 a4                    value-of-a4