title: How to plot bivariate normal distribution with expanding ellipses
body: <p>How to plot  bivariate normal distribution with expanding ellipses and add 5%, 25%, 50%, 75% and
  95% label in the plot? Thank you!</p>
  
  <p><img src="https://i.stack.imgur.com/q6tP4.jpg" alt="enter image description here"></p>