This is a good basic template for drawing a tikz picture tree.

latex_Tree.tex

% place in preamble:
%\usetikzlibrary{trees}
%\usetikzlibrary{decorations.text}
\begin{figure}[htb]
\centering
\ffigbox[\FBwidth]{\caption{Alliance Decisions in An incomplete information framework}
\label{}}{

\begin{tikzpicture}
% various formatting follows:
[font=\footnotesize, 
       grow=right,
                   level 1/.style={sibling distance=6em},
                   level 2/.style={sibling distance=1em}, level distance=3cm,
                   level 3/.style={sibling distance=5em}]

% begin tree
  \node[circle,draw] (N) {N} %  root
  % nature pushes to holder on right (reliable type)
% BEGIN RIGHT SIDE
    child [grow=right]{
      node (reliable_holder) {Holder}
% BEGIN UPPER RIGHT SIDE
      child [grow=up]{
        node (reliable_signaled) {Observer} 
        child{ 
          node (reliable_signaled_accept){$(x+y,z)$}
          edge from parent node [right] {accept}
        }
        child{
          node (reliable_signaled_reject){}
          edge from parent node [left] {reject}
        }
       } 
% UPPER RIGHT SIDE END
% BEGIN LOWER RIGHT SIDE
      child [grow=down]{
        node (reliable_not_signaled) {Observer}
        child[]{
          node (reliable_not_signaled_reject) {} 
          edge from parent node [left] {accept}
        }
        child[]{
          node (reliable_not_signaled_accept) {}
          edge from parent node [right] {reject}
        }  
      }
    }
% LOWER RIGHT SIDE END
% RIGHT SIDE END
% BEGIN LEFT SIDE
    child[grow=left]{node(unreliable_holder){Holder}
      % BEGIN UPPER LEFT SIDE
      child [grow=up]{
        node (not_reliable_signaled) {Observer}
        child{
          node {}
          edge from parent node[right] {reject} 
        }
        child{
          node {}
          edge from parent node[left] {accept}         
        }
      }
      % UPPER LEFT SIDE END
      % BEGIN LOWER LEFT SIDE
      child [grow=down]{node (not_reliable_not_signaled) {Observer}
        child{
          node (not_reliable_not_signaled_reject) {}
          edge from parent node [left] {accept}
        }
        child{
          node (not_reliable_not_signaled_accept) {}
          edge from parent node [right] {reject}
        }
      }
      % LOWER LEFT SIDE END
    }
%LEFT SIDE END
;
\draw[dashed] (not_reliable_not_signaled) -- (reliable_not_signaled)  
  node[midway,above] {};

\draw[dashed] (not_reliable_signaled) -- (reliable_signaled)  
  node[midway,above] {};


\path (N) edge node[above]{$Pr($reliable $)$} node[below]{$\lambda$} (reliable_holder);
\path (N) edge node[above]{$Pr(\neg$ reliable $)$} node[below]{$1-\lambda$} (unreliable_holder);
\path (unreliable_holder) edge node[left, sloped=false]{signal} (not_reliable_signaled);
\path (unreliable_holder) edge node[left ,sloped=false]{$\neg$ signal} (not_reliable_not_signaled);
\path (reliable_holder) edge node[right, sloped=false]{signal} (reliable_signaled);
\path (reliable_holder) edge node[right ,sloped=false]{$\neg$ signal} (reliable_not_signaled);


\end{tikzpicture}

  
}
\end{figure}