Try following code
function Fname($parentId=0){
$catgArray = array();
$sql = mysql_query("SELECT * FROM Table Where Cat_PID=$parentId");
$mainCatg = mysql_fetch_array($sql);
foreach($mainCatg as $mc){
array_push($catgArray , $mc);
$subCatg = $this->Fname($mc->Cat_ID);
if (count($subCatg ) > 0) {
array_push($catgArray , $subCatg );
}
}
return $catgArray;
}
In the Result we can check the sub category levels by using is_array() function