use ChemBioDraw and your EI fragments starting from mother molecule to the ancestries, remove groups one by one and match with your fragment using this technique you can build your chart of fragmentation 

Dear Somnath,

Since, you already have mass spectrum of each of your compound of interest. You may directly match your recorded spectra with available libraries if installed in your mass spectrometer.  I am sure that the  resultant hits (library) will be very much correct as these compounds are already known.

If you are willing to understand in detail about mass spectral fragmentation technique specific to type of functional groups, you should consult textbooks like Spectrometric Identification of Organic Compounds by Robert M. Silverstein, Francis X. Webster, David J. Kiemle, David L. Bryce etc.

Otherwise, attachment named terpene by Mr. Raj is also useful in order to understand this concept.

Good Luck

Thank you for your kind answers. I identified the compound. I identified the molecular weight of different fragments from a specific compound as well. But it's hard to determine the structure of fragments from their chemical formula

Interesting question