Help with XSLT mapping

Hi

I have a file that produces a flat xml as below

01 header                         => invoice 1

02 vendor data

03 vendor bank data

04 gl line data

01 header                          => invoice 2

and so on.

I am struggling with creating an xsl template that will convert the above xml into a parent-child relationship as below

01 header

===> 02 vendor data

===> 03 vendor bank data

===> 04 gl line data

01 header

Basically I want to insert all 02,03,04 nodes that follow a 01 node as children of the 01 node, until the next 01 node, and so on till the end of file.

Please can experts provide me the appropriate xsl template to process the file as desired.