    [1]-[2]-[3]
            /
     [4]-[5]
      \
     [6]-[7]-[8]-[9]-[10]
     |   /              /
     [11]    [12]-[13]-[14]
               \   /
        [15]-[16]-[17]
          |
          [18]-[19]-[20]
               / \
            [21]-[22]
            /
           [23]     [26]-[27]-[28]
            \        /         |
             [24]-[25]       [29]
                              /
                             [30]
