+---------+            +---------+
                |   PE1   |            |   PE2   |
 +---+          |  +---+  |  +------+  |  +---+  |            +---+
 |CE1+---AC1----+--|BD1|  |  |      |  |  |   |--+----AC2-----+CE2|
 +---+  (Root)  |  |   |  |  |      |  |  |BD1|  |   (Leaf)   +---+
                |  +---+  |  |      |  |  |   |  |            +---+
                +---------+  | MPLS/|  |  |   |--+----AC3-----|CE3|
                             |  IP  |  |  +---+  |   (Leaf)   +---+
                             |  Net |  +---------+     
                             |      |
                             |      |  +---------+
                             |      |  |   PE3   |
                             |      |  |  +---+  |            +---+
                             +------|  |  |   |--+----AC4-----+CE4|
                                       |  |BD1|  |   (Leaf)   +---+
                                       |  |   |  |
                                       |  +---+  |
                                       +---------+