$ sudo apt-get remove fasttree 

Uninstall fasttree including dependent package

If you would like to remove fasttree and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove fasttree 

Use Purging fasttree

If you use with purge options to fasttree package all the configuration and dependent packages will be removed.

$ sudo apt-get purge fasttree 

If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.

$ sudo apt-get purge --auto-remove fasttree 

See Also,