A single IdMapper's ID node.
| Node | *top | The parent node. |
| Node | *left | The left subnode. |
| Node | *right | The right subnode. |
| int | balance | Node's balance (see AvlTree::Node for details. |
| unsigned long | weight | Node's weight (total number of nodes in both subtrees). |
| unsigned long | value | Node's value (the allocated identificator). |
| void | *data | User's data associated with this node. |