Here are two parse trees for string if ( true ) if (true) x else x.

           ---S---                    
          /|  |  |\ 
         / |  |  | \  
        /  |  |  |  \
       /   |  |  |   \
     if    (  E  )   ------S-------
              |     /|  |  |  |  | \
            true   / |  |  |  |  |  \
                  /  |  |  |  |  |   \
                if   (  E  )  S else  S
                        |     |       |
                      true    x       x
            
        ------S-------
       /|  |  |  | |  \
      / |  |  |  | |   \
     /  |  |  |  | |    \
    if  (  E  )  | else  S
           |     |       |
         true    |       x
              ---S---                    
             /|  |  |\ 
            / |  |  | \  
           /  |  |  |  \
          /   |  |  |   \
        if    (  E  )    S
                 |       |
               true      x