This plant seems Mycetia longifolia of Rubiaceae family.

Please see the attach picture, which seem to be similar of your, I am not sure but it seems to be Mycetia javanica 

See the below link

http://www.phytoimages.siu.edu/cgi-bin/dol/dol_terminal.pl?taxon_name=Mycetia_javanica&rank=binomial

http://www.phytoimages.siu.edu/imgs/pelserpb/r/Rubiaceae_Mycetia_javanica_110274.html

Please also check the plant as Mycetia mukerjiana. The species Mycetia longifolia is very common in Northeastern states of India including Tripura.

Please have a look at this researchgate link also. I think this link may be helpful in identification.

https://www.researchgate.net/post/help_seek_for_plant_identification

Mycetia longifolia (Wall.) Kuntze is correct answer by Dr. Arvind. In  Mycetia javanica (Blume) Reinw. ex Korth. the size of peduncle and pedicel is less. 

Thanks Rajeev for confirming the identification.