Steps

1. Click on 'upload' button from the top left side panel and select "Bulk Upload" option from drop down menu.
2. Select a folder to place the document from the left side panel.
3. Select 'files to upload' option and a dialog will appear.
4. Select multiple files from the open dialog and click 'OK'.
5. Click on 'Upload' button, the files will get uploaded to the selected folders.

Note: To select multiple files, Please hold down Shift or Ctrl key.