Y-------T
            |       |   
            |       |    
            |       |    
        Y---T       U---Y
       /     \     /     \
  V---T       O---O       U---Y
  |   |       |   |       |   |
  |   |       |   |       |   |
  |   |       |   |       |   |
  Y---V-------O---O-------W---U 
  |   |       |   |       |   |
  |   |       |   |       |   |
  |   |       |   |       |   |
  *---Y       O---O       Y---*
 /     \     /     \     /     \
*       V---O       O---W       *
        |   |       |   |
        |   |       |   |
        |   |       |   |
        Y---V-------W---Y
        |   |       |   |
        |   |       |   |
        |   |       |   |
        *---Y       Y---*
       /     \     /     \
      *       V---W       *
              |   |
              |   |
              |   |
              W---Y
              |   |
              |   |
              |   |
              *---*
             /     \
            *       *