Grouping Tree Cols

Hi,

I want to group certain columns within the columns in a <treecols> tag
Is that possible? If so, how?

What I really want to achieve, is something that looks like this:

Name        |          GROUP 1          |          GROUP 2
|          GROUP 3          |
                 |    Col1     |     Col 2      |    Col3     |    Col
4       |            Col 5              |
John          |      1        |          2       |      3
|       4         |             5                   |
Matt          |      3        |          4       |      7
|       7         |             3                   |

Right now I have:
Name        |    Col1     |     Col 2      |    Col3     |    Col
4       |            Col 5              |
John          |      1        |          2       |      3
|       4         |             5                   |
Matt          |      3        |          4       |      7
|       7         |             3                   |

Is there a way of achieving this?

Thanks,
AI