size(400, 400);

int numLevels = 10;
float stepSize = width/numLevels;

for (int level = 0; level < numLevels; level += 1) {
  float start = (numLevels-level-1)*stepSize/2;
  for (int block = 0; block < 1+level; block++) {
    rect(start + block*stepSize, level*stepSize, stepSize, stepSize);
  }
}