php - Implementing another list dropdown upon extra selection -

i have mysql database, , have option displays 'treatments' dropdown box on html page. how go implementing code, if user wants select more 1 treatment, dropdown box appear?

edit: e.g. lets shopping items online, , have items listen in dropdown box. pick one, , want pick more. click: 'add more' , dropdown appears on page can select item.

here php code:

<?php  $hostname = 'hostname'; $dbname = 'dbname'; $username = 'username'; $password = 'password';  $con=mysql_connect($hostname,$username,$password,$dbname) or die("failed connect mysql: " . mysql_error()); $db=mysql_select_db($dbname,$con) or die("failed connect mysql: " . mysql_error());   $query = "select * `treatments`";  $result = mysql_query($query, $con); $options = "";  if (!$result){     die("no results found."); }  while ($row = mysql_fetch_array($result)){     $options .= "<option>$row[1]</option>"; }   ?> 

actually need make multiselect drop down. if add multiple = "multiple" html tag drop down used multi select.

<select name="anyname[]" multiple>   <?php   while ($row = mysql_fetch_array($result)){     echo "<option>$row[1]</option>";  }  ?> </select> 

for more need link. jquery multiselect drop down menu

hope you.

thanks