Answer
See image:
Work Step by Step
In the plane xy, ($z=0)$ the surface leaves an ellipse as a trace.
$\displaystyle \frac{x^{2}}{3^{2}}+\frac{y^{2}}{6^{2}}=1$
Draw several such ellipses in planes parallel to xy.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.