3D Cone

\usepackage{tikz-3dplot}
\tdplotsetmaincoords{70}{120}

\begin{tikzpicture}[tdplot_main_coords]
  \draw[thick] (0,0,0) -- (0,0,3);
  \draw[thick] (0,0,0) ellipse (1.2 and 0.4);
  \draw[thick] (1.2,0,0) -- (0,0,3);
  \draw[thick] (-1.2,0,0) -- (0,0,3);
\end{tikzpicture}