size(600, 600);

int numLevels = 5;
float stepSize = height/(1+numLevels);

beginShape();
// right side from top to bottom
for (int level = 0; level < numLevels; level++) {
  vertex(width/2+0.5*stepSize*(1+level), stepSize * (0.5+level));
  vertex(width/2+0.5*stepSize*(1+level), stepSize * (1.5+level));
}

// left side from bottom to top
for (int level = numLevels-1; level >= 0; level--) {
  vertex(width/2-0.5*stepSize*(1+level), stepSize * (1.5+level));
  vertex(width/2-0.5*stepSize*(1+level), stepSize * (0.5+level));
}
endShape(CLOSE);