public void drawTree(Graphics g) {
        g.setColor(Color.red);
        int halfWidth = cellWidth / 2;
        if (showTree) {
            for (Edge e : this.maze.mst) {
                g.drawLine(e.from.x * cellWidth - halfWidth,
                        e.from.y * cellWidth - halfWidth,
                        e.to.x * cellWidth - halfWidth,
                        e.to.y * cellWidth - halfWidth);
            }
        }
    }