How to insert multiple selects into separate rows

Having read several posts on this subject, I have managed to insert data from a multiple select form.However, the data goes into one row. I need each value to go into separate rows.Here is the relevant field in the form

<p><label>Assign Users::</label><select id="client" name="client[]"  multiple="multiple"><option  class="multiple" value="selected">Assign User to Project</option><?php             foreach($clients as $client){         ?><option value="<?php echo $client ->user_id;?>"><?php echo $client ->user_name; ?></option><?php         }        ?></select></p>

And here is the Insert code

$ref=$_POST['project_ref'] ;$user_id=implode(',', $_POST['user']);$wpdb->insert( 'vo_wp_assigned_projects', array('client'=>$user_id,'project'=> $ref));

This inserts into one row, which is no use as I need to be able to access each individual entry.I have tried foreach loops from other posts in this group with no success.I hope I have provided sufficient information.