Hello sir, Tongue bleeding is not common . Causes of tongue bleeding may be oral herpes which in initial stages may be a cold sore and may cause bleeding on any trigger,any sharp tooth impinging on tongue, hemangioma , cystic hygroma,may also be due to low platelet count which may cause bleeding. Please consult a dentist soon  know the cause get it treated.

The bleeding maybe coming from gums and not the tongue. Get a dental check up to diagnose properly