Because there was no Pushbullet application for Ubuntu, Lorenzo from atareao.es (you may already know some of his work: My Weather Indicator, Calendar Indicator, Touchpad Indicator, Nautilus/Nemo image tools, etc.) has created a Pushbullet AppIndicator for Ubuntu.
Install Pushbullet Indicator in Ubuntu
sudo add-apt-repository ppa:atareao/atareao sudo apt-get update sudo apt-get install pushbullet-indicator
How to setup and use Pushbullet Indicator
… and finally enter what you’d like to send and click OK.