Hello Kajal,
 
To show only top level categories in autosearch. Please try to edit the file “app/code/community/Ves/Autosearch/Block/Autosearch.php”
Then find code:
if($subcats != ”){
$html .= $this->getTreeCategories($category->getId(), (int)$level + 1, $caret.’ ’);
}
 
Remove it or comment it.