I am trying to create something like the picture below, here is the code I have so far but it will not render I am not sure where I am going wrong.
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\begin{document}
\begin{tikzpicture}[
vertex/.style = {shape=circle,draw,minimum size=2em},
edge/.style = {->,-Latex},
]
% Vertices
\node[vertex] (c) at (0,0) {6};
\node[vertex] (a) at (-2,-2) {};
\node[vertex] (b) at (2,-2) {};
\node[vertex] (d) at (0,-3) {6};
\node[vertex] (e) at (-1,-5) {?};
\node[vertex] (f) at (1,-5 {?};
\node[vertex] (g) at (-2,-7) {};
\node[vertex] (h) at (0,-7) {5};
\node[vertex] (i) at (2,-7) {};
\node[vertex] (bx) at (0,-9) {5};
% Edges
\draw[edge, ultra thick] (a) -- (c) node[midway,left] {$\times$} ;
\draw[edge, ultra thick] (b) -- (c) node[midway,right] {$\times$} ;
\draw[edge, ultra thick] (g) -- (bx) node[midway,left] {$\+$} ;
\draw[edge, ultra thick] (I) -- (bx) node[midway,right] {$\+$} ;
\draw[edge, ultra thick] (a) -- (i) node[midway,left] {} ;
\draw[edge, ultra thick] (b) -- (g) node[midway,right] {} ;
\end{tikzpicture}
\end{document}