documentclass[tikz,margin=5pt]{standalone}
begin{document}
begin{tikzpicture}[line width=0.3mm]
node at (1,1) (A) {A};
node at (2,3) (B) {B};
node at (3,4) (C) {C};
draw [<->] (A)--(B);
draw [<->] (A)--(C);
end{tikzpicture}
end{document}