Indent children nodes in XSL-FO

I have XML structure like this

<TestLog>
   <TestLogItem id="0" pid="-1">
      <Message>some message</Message>
   </TestLogItem>
   <TestLogItem id="1" pid="0">
      <Message>some message</Message>
   </TestLogItem>
   <TestLogItem id="2" pid="0">
      <Message>some message</Message>
   </TestLogItem>
   <TestLogItem id="3" pid="2">
      <Message>some message</Message>
   </TestLogItem>
</TestLog>

Every TestLogItem node has "id" and "pid(parentId)". I am showing the messages in table rows and just want to indent every message if its a child of previous node i-e its PID is equal to previous node ID. I cannot figure out how to do it in xsl-fo to convert it to pdf.

Any TestLogItem node can have any number of TestLogItem children nodes.