A most common tree one can come across in Indian subcontinent is Neem. An excellent herb that prevents Bacterial and Fungal infections. Keeping this plant at home drives Mosquitoes and diseases that spread through Mosquitoes away. The leaves are quite bitter but chewing even a tiny bit has enormous health benefits! More than 130 biologically active compounds are found in this plant. Excellent medicine for Skin problems, Immune system, Cardiovascular disease, diabetes and liver problems. Strongly recommended to grow one on your backyard if you can!
Scientific information about this herb can be found here: http://www.rjpbcs.com/pdf/2012_3(1)/15.pdf