\documentclass{standalone}
\usepackage{tikz}
\begin{document}
	\begin{tikzpicture}
	\draw[fill=blue!10] (-2, 3.5) --(-0.4, 1.8)--(0,2.8) --cycle;
	\draw[fill=blue!10] (-2, 3.5) --(-0.4, 1.8)--(0,0) node[anchor=north]{$x_1$}--cycle;
	\draw[fill=blue!10] (-0.4, 1.8)node[anchor=south]{$y_3$}--(0,0) --(0.4,1.8)--cycle;
	\draw[fill=blue!10] (2, 3.5) --(0.4, 1.8)--(0,0) node[anchor=north]{$x_1$}--cycle;
	\draw[fill=blue!10] (2, 3.5) node[anchor=west]{$x_3$}--(0.4, 1.8)node[anchor=south] {$x_2$}--(0,2.8) node[anchor=north]{$y_1$}--cycle;
	\draw[fill=blue!10] (-2,3.5) node[anchor=east]{$y_2$}--(0,2.8)--(2,3.5)--cycle;
	\draw (-0.9,2.7) node{$\sigma_1$};
	\draw (-0.7,1.6) node{$\sigma_2$};
	\draw (0,0.9) node{$\sigma_3$};
	\draw (0.7,1.6) node{$\sigma_4$};
	\draw (0.9,2.7) node{$\sigma_5$};
	\draw (0,3.2) node{$\sigma_6$};
	\draw (-0.4, 1.8)--(-2, 3.5)--(0,2.8);
	\draw  (0,0)--(0.4,1.8)--(2,3.5);
	\draw (-0.4, 1.8)--(0,0);
	\draw (0, 2.8)--(2, 3.5);
	%\draw [thick, green](-0.4, 1.8)--(0,0);
	%\draw [thick, green](0, 2.8)--(2, 3.5);
	\end{tikzpicture}
\end{document}
