private Node makeSiblings(Node node, Node sibling) {
int parentLevel = MAX_BITS - Long.numberOfLeadingZeros(node.bits ^ sibling.bits);
Node parent = createNode(node.bits, parentLevel, 0);
// the branch is given by the bit at the level one below parent
long branch = sibling.bits & parent.getBranchMask();
if (branch == 0) {
parent.left = sibling;
parent.right = node;
} else {
parent.left = node;
parent.right = sibling;
}
return parent;
}
