23     //     | parent node |  n--> | current node |  in MergeInsertInternal()
28     // suppose current node is parent node's left child, then  in MergeInsertInternal()
29     // n points to the current node,  in MergeInsertInternal()
31     TreapNode* current = root_;    // root is current node  in MergeInsertInternal()  local
33     // stack of pn recording how to go from root to the current node  in MergeInsertInternal()
38         if (current == nullptr) {  in MergeInsertInternal()
39             current = new (nodeAllocator_.Allocate()) TreapNode(idx, num, refreshRegionDesc);  in MergeInsertInternal()
40             CTREE_ASSERT(current != nullptr, "fail to allocate a new node");  in MergeInsertInternal()
41             *pCurrent = current;  in MergeInsertInternal()
45         MergeResult res = MergeAt(*current, idx, num, refreshRegionDesc);  in MergeInsertInternal()
52         if (m < current->GetIndex()) {  in MergeInsertInternal()
55             pCurrent = &(current->l);  in MergeInsertInternal()
56             current = current->l;  in MergeInsertInternal()
57         } else if (idx > current->GetIndex() + current->GetCount()) {  in MergeInsertInternal()
60             pCurrent = &(current->r);  in MergeInsertInternal()
61             current = current->r;  in MergeInsertInternal()
73         current = *pCurrent;  in MergeInsertInternal()
74         CTREE_ASSERT(current, "merge insertion bubbling failed case 1");  in MergeInsertInternal()
75         if (m < current->GetIndex()) {  in MergeInsertInternal()
77             if (current->GetCount() < current->l->GetCount()) {  in MergeInsertInternal()
78                 *pCurrent = RotateLeftChild(*current);  in MergeInsertInternal()
83         } else if (idx > current->GetIndex() + current->GetCount()) {  in MergeInsertInternal()
85             if (current->GetCount() < current->r->GetCount()) {  in MergeInsertInternal()
86                 *pCurrent = RotateRightChild(*current);  in MergeInsertInternal()