It is possible to have both MySQL servers running on the same machine but, it'll take some work.
First you would need to install 5.7 in a different directory than 5.5. Also since MySQL uses a default port, you would need to run 5.7 on a different port.
You're basically creating an entire new MySQL server
update-alternatives is a program that could work for you as well. (I have not tested this)
update-alternatives --install /usr/bin/mysql-server mysql-server /usr/bin/mysql-5-1/bin/mysql-server 10
update-alternatives --install /usr/bin/mysql-server mysql-server /usr/bin/mysql-5-6/bin/mysql-server 10
--install adds a new mapping
/usr/bin/mysql-server is the link location (where mysql-server normally is located)
mysql-server is the name of the mapping
/usr/bin/mysql-5-6/bin/mysql-servera is where I placed the new version of mysql-server
10 is the priority
You then choose which version of mysql-server you want like so
update-alternatives --set mysql-server /usr/bin/mysql-5-6/bin/mysql-server