Two datasets inside a same tablix

<div class="row" style="width: 800px; overflow: visible;">Using SSRS , need to generate report, here i have two datasets one for main display & second dataset for displaying 2 sub categories of first datasets.

So the output will be, first dataset's each row may or may not contain its respective 2 sub categories[second dataset].

so here i need to display main row with its repective 2 sub catgories if present for that main row.

Any idea of how to display as Main dataset as Parent row with its repective 2 sub categories row next to it if present

two datasets used also is their possible to display with two tablix , one tablix present inside other or so

sample output :

1 , parent row1
Child 1
child 2
parent row2 ----- in case of no child , child 6, child 7 will not be displayed , only Parent row2 alone displayed
Child 6
child 7
parent row3
Child 3
child 4</div> <div class="row" style="width: 800px; text-align: right;">Edit  Abuse</div><div class="newlinesmall"></div> <div style="margin: 0px; padding: 0px 0px 0px 0px; background: url('/images/NullSkullFooterBackground.png') repeat left top; bottom: 0px; height: 80px; float: left; position: fixed; width: 100%;"> <div style="margin: 0 auto; vertical-align: middle; padding: 0px 0px 0px 7px; width: 1250px; height: 80px; background: url('/images/NullSkullFooter.png') no-repeat left top;"></div> </div>