Multiple Image Upload PHP form with one input

Question

I want to have multiple image upload forms with only using one input.

The upload.php:

<?php
include("../include/session.php");

session_start();
$allowedExts = array("jpeg", "jpg", "png", "gif");
$extension = end(explode(".", $_FILES["upload"]["name"]));

if(isset($_FILES['upload']['tmp_name']))
{
    for($i=0; $i < count($_FILES['upload']['tmp_name']);$i++)
    {

        if (($_FILES["upload"]["name"] < 90000000000000000)
            && in_array($extension, $allowedExts)) {
                if ($_FILES["upload"]["error"] > 0)
                {
                    header('location: '.$error); die;
                }
                else
                {

                    if (file_exists("../icons/".$_SESSION["username"] ."/" . $_FILES["upload"]["name"]))
                    {
                    echo "error";
                    }
                    else
                    {
                        if(!is_dir("../icons/". $_SESSION["username"] ."/")) {
                            mkdir("../icons/". $_SESSION["username"] ."/");
                        }

                        $temp = explode(".",$_FILES["upload"]["name"]);
                        $file = rand(1,999999999999) . '.' .end($temp);

                        move_uploaded_file($_FILES["upload"]["tmp_name"], "../icons/". $_SESSION["username"] ."/". $file);  
                    }
                }
            }
        } else {
            echo "yep error";
        }
    }
} 
?>

If I take out the lines:

if(isset($_FILES['upload']['tmp_name']))
{
    for($i=0; $i < count($_FILES['upload']['tmp_name']);$i++)
    {

This works but only allows me to upload once. Can someone please guide me on making this work?