Do you mean playing the same file twice simultaneously? If so, yes, you would need to create 2 streams for it, eg. 2 BASS_StreamCreateFile calls. Or if it's a short file, you might use the sample functions instead, something like this...
HSAMPLE sample = BASS_SampleLoad(FALSE, "hello-3.mp3", 0, 0, 2, 0); // load the file as a sample
HCHANNEL chan1 = BASS_SampleGetChannel(sample, 0); // get a playback channel
HCHANNEL chan2 = BASS_SampleGetChannel(sample, 0); // and another one
Please see the documentation for details on those functions.