Add the Repo:
wget http://repo.mysql.com/mysql-apt-config_0.2.1-1debian7_all.deb
dpkg -i mysql-apt-config_0.2.1-1debian7_all.deb
The above package will create a file /etc/apt/sources.list.d/mysql.list which will contain lines like these or similar:
deb http://repo.mysql.com/apt/debian/ wheezy mysql-5.6
deb-src http://repo.mysql.com/apt/debian/ wheezy mysql-5.6
Install mysql 5.6:
apt-get update
apt-key adv --keyserver hkp://pgp.mit.edu:80 --recv-keys 5072E1F5
apt-get install mysql-server-5.6