We are developing a compact wide-angle imaging detector for MeV gamma-rays using stacked BGO scintillator rods to apply to neutron induced prompt gamma-ray analysis (NPGA), which is one of the promising methods for non-destructive detection of hidden explosives by measuring characteristic gamma-rays produced from chemical elements. The gamma-ray imaging in NPGA applications is also necessary to locate them and improve the signal-to-noise ratio. A compact wide-angle imaging detector has an advantage in detection efficiency, because it can take images at short distance from inspection objects. For a compact wide-angle imaging detector for MeV gamma-rays, we have proposed the image reconstruction technique based on the statistical estimation algorithm using stacked BGO scintillator rods that can get information on energies and 3D positions. In this paper, we mainly discussed an information processing method for recorded signals especially to provide the additional function rejecting pile-up events, which makes our detector possible to operate in high dose filed. Through the EGS4 simulations modeling our detector units, we successfully demonstrated that the pile-up events can be suppressed by picking out only events with small spatial deviation of scintillation positions. In addition, we experimentally demonstrated nitrogen imaging based on NPGA using our gamma-ray detector.