A comprehensive particle based integrated code including atomic and relaxation processes has been developed. By using the code, we have investigated the lightning process of compressed neon gas that in a uniformly applied electric field. After a long time interval, streamers are slowly developed from a tiny ionization spot that is initially set. Then a complicated branching is suddenly and also explosively triggered, leading to fine net-like structures or sprites. Electromagnetic radiations are emitted from the sprite and show a low-power wave number spectrum, suggesting that the sprite exhibits a fractal nature.