<input type="file" name="file" multiple/>
The multiple attribute is new in HTML5 (Reference)
Here is a reference for multiple
Versions supporting `multiple` attribute
Chrome Edge Firefox Opera Safari
6.0 10.0 3.6 11.0 5.0
Why it doesn't work with Internet Explorer ?
Uploading multiple files is a specific part of HTML5 that none of the Internet Explorers support. Here is a reference to it. Though , IE 10.0 has started supporting it.
I found some related resources here and here
According to all above statistics , I might like to suggest you to read the second post of this which uses certain alternatives of multiple attribute :
If you can't or don't want to use multiple INPUT TYPE=FILE controls, you must use Flash or Silverlight or a custom ActiveX control