→ apt-cache policy mate-desktop-environment
mate-desktop-environment:
  Installed: (none)
  Candidate: 1.14.0+2~xenial1.2
  Version table:
     1.14.0+2~xenial1.2 500
        500 http://ppa.launchpad.net/ubuntu-mate-dev/xenial-mate/ubuntu xenial/main amd64 Packages
        500 http://ppa.launchpad.net/ubuntu-mate-dev/xenial-mate/ubuntu xenial/main i386 Packages
     1.12.0+1 500
        500 file:/media/Linux/apt-repo/xenial-mate  Packages
        500 file:/media/Linux/apt-repo/xenial3  Packages
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe i386 Packages

sudo apt-add-repository ppa:ubuntu-mate-dev/xenial-mate
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install mate-dock-applet