[ubuntu] Lost all my life's data while installing ubuntu

Hi

Please help I really need an advice.

I am a new user of Ubuntu and installed successfully but while installing made a life's big mistake.

Scenario

I was installing Ubuntu through USB while my exteal HDD was attached to the laptop.

Ubuntu picked the exteal HDD (3 TB) and I have installed ubuntu on my exteal HDD (By Mistake) and the operating system (ubuntu) formated my exteal HDD and installed the ubuntu operating system.

Now all my life's data was on my exteal drive.

After installation I have not touched my exteal HDD through any software.

Please advice, will be waiting for your expert advice.

Thanks