If your sample is small and your RNA is pure, it may be difficult to see a pellet but that doesn't mean the RNA is not there. Have you tried resuspending that invisible pellet and analysing your sample in a Nanodrop or similar?

We use RNeasy Plant kit (Qiagen) with good results from many different plant samples.

For isolation of RNA generally very small amount of sample is been taken.If the pellets are not visible no problem add  known primers you may get the bands and confirm.

Are you grinding tissue in liquid Nitrogen before adding Trizol?

I assume you are transferring upper aqueous phase to new tube before adding Isopropanol?

If you really want to see your pellet, you can add one microliter of glycoblue to your aqueous phase before alcohol precipitating.

Thanks a lot all...

Dear Torikul Islam!

I recommend you method for isolation RNA using 2-methoxyethanol and cetavlon. This method is widely used to obtain nucleic acid (DNA or RNA) highly purified from polysaccharides that are components of animal, plant and bacterial cells.

I propose to your attention many works in which this method was used, for example:

Jones A.S. The isolation of bacterial nucleic acids using cetyltrimethlyammonium bromide (cetavlon). Biochim. Biophys. Acta. 1953.10: 607-612; 

JONES A.S., MARSHG E. & RIZVIS B.H. The Isolation and Composition of the Nucleic Acids of Aerobacter aerogenes J . gen. Microbiol. 1957. 17: 586-595;

Biggin W.P. An investigation of RNA induction in amphibian tissues. B.Sc. (Honours), The University of British Columbia, 1966; 

Naktinis V.I., Maleeva N.E., San'ko D.F., Mirzabekov A.D. Two simple methods for isolation of DNA from various sources using cetavlon. Biokhimiia. 1977. 42(10):1783-90;

as well as my published work:

Tsygankova V.A., Zayets N.N., Galkina L.A., Prikazchikova L.P., Blume Ya.B., An unusual minor protein appearing in embryonic axis cells of haricot bean seeds following germination process stimulated by 6-methylthiouracyl. Biopolymery and Cell (Ukr.), 1998, vol. 14(5), pp. 438-448:

https://www.academia.edu/3239206/An_unusual_minor_protein_appearing_in_embryonic_axis_cells_of_haricot_bean_seeds_following_germination_process_stimulated_by_6-methylthiouracil

 Sincerely yours, ScD Victoria Tsygankova

Whether you could see the pellet or not depends on the amount of tissue that you used.

I used to get ~10 µg total RNA from 4-day-old etiolated Arabidopsis seedlings, which grew from about 100 seeds, with the RNeasy Plant kit. This kit is a bit expensive but one of the best RNA extraction kits that I've used, particularly the buffers are very good to purify total RNA from etiolated seedlings. If you would like to save money, you can combine the buffers from Quagen and some cheap columns from other companies.

If you use RNA extracted with Trizol for qRT-PCR or other sensitive applications, I recommend that you purify your RNA with columns, because the residual phenol disturbs enzymatic reactions.