BZIP2 multiple files without losing original files

I want to bzip2 about 1000 files. However, I am tasked to not remove the old files and leave both the original and its bz2 file in the same folder. What is the quickest way to do this. Just to rephrase my question, suppose I have file1.txt, file2.txt, file3.txt...file1000.txt, I would need its bz2 versions in the same folder without removing them. How to achieve this?