##Tree Implementations
LinkedTree - a mutable, not thread safe tree
TreeNodeImpl - an immutable tree
MutableTreeNodeImpl - a mutable tree that does not preserve modification order
BinaryTreeWrapper - an immutable binary tree
MutableBinaryTreeImpl - a mutable binary tree
BinarySearchTree - a mutable binary search tree
PathCopyTree - a path copy tree that uses a separate data structure for the back references between nodes