What does it mean to have a bladder inside a bladder? is there a treatment?

Possibly.: I'm not sure exactly what you mean, but there are conditions where outpouchings of bladder tissue can appear as a fluid-filled cavity within the bladder. Ureteroceles are swellings of the bladder lining around the ureter, & can lead to urinary infections or bladder blockage. These can be incised or removed. Bladder diverticuli bulge out from the bladder, and may appear to be a "second" bladder.