+
                        A / \ A
                         /   \
                        +-----+
                     B / \   / \ B
                      /   \ /   \
                     +-----+-----+
                  C / \   / \   / \ C
                   /   \ /   \ /   \
                  +-----+-----+-----+
               D / \   / \   / \   / \ D
                /   \ /   \ /   \ /   \
               +-----+-----+-----+-----+
            E / \   / \   / \   / \   / \ E
             /   \ /   \ /   \ /   \ /   \
            +-----+-----+-----+-----+-----+
         F / \   / \   / \   / \   / \   / \ F
          /   \ /   \ /   \ /   \ /   \ /   \
         +-----+-----+-----x-----+-----+-----+
      G / \   / \   / \   / \   / \   / \   / \ G
       /   \ /   \ /   \ /   \ /   \ /   \ /   \
      +-----+-----+-----+-----+-----+-----+-----+
   H / \   / \   / \   / \   / \   / \   / \   / \ H
    /   \ /   \ /   \ /   \ /   \ /   \ /   \ /   \
   +-----+-----+-----+-----+-----+-----+-----+-----+
I / \   / \   / \   / \   / \   / \   / \   / \   / \ I
 /   \ /   \ /   \ /   \ /   \ /   \ /   \ /   \ /   \
+-----+-----+-----+-----+-----+-----+-----+-----+-----+
   1     2     3     4     5     6     7     8     9