type ImmutableTree struct {
	root                   *Node
	ndb                    *nodeDB
	version                int64
	nonce                  int64             // new field to track the current ID
	skipFastStorageUpgrade bool
}

type Node struct {
	key           []byte
	value         []byte
	hash          []byte

	leftHash      []byte        
	rightHash     []byte    

	nodeKey       int64         // new field which reflects the current node key
	leftNodeKey   int64       // new field
	rightNodeKey  int64      // new field

	version       int64           // possible to remove ???

	size          int64
	leftNode      *Node
	rightNode     *Node
	subtreeHeight int8
	persisted     bool
}