Difference between .bz2 and .tar.bz2 files

I am supposed to find whether a file is compressed using .bz2 or .tar.bz2(without using extension of file) and and decompress it accordingly. I used the file command but it is giving same result for both .bz2 and .tar.bz2. Please suggest a way to identify .bz2 and .tar.bz2 files distinctly.