Self-organized pattern formation is observed in bacterial colony growth. Recently reported knotted-branching pattern of Bacillus circulance colony consists of the trajectories of aggregates which grow, move and reproduce simultaneously. We modelled these processes by combining reaction diffusion system of nutrient dynamics, nucleation theory for aggregate generation and individual based dynamics of the motion and growth of aggregates. The branching pattern produced by computer simulation shows great similarity with experiments. Response to the initial nutrient concentration is also consistent with the experiments.