In this study, a method for modeling trees with rugged surfaces by simulating tree growth is proposed. The phenomena of cell division is considered for simulating tree growth. There are two types of cells that affect the growth of trees, namely, the apical meristem cells and the cambium cells. The former cells lie at the apex of a branch and are responsible for the extension of the branch. The latter cells cover the surface of the tree and are responsible for its lateral growth. Further, knots are generated by unusual and uneven growth of the cambium cells. To simulate these phenomena, a tree is modeled as a polygon mesh which grows by displacing the vertices of the mesh. Each vertex acts as an apical meristem cell or a cambium cell. The tree growth is defined by an LSystem. Subsequently, tree models with rugged surfaces, such as those including knots, are generated.