A hierarchical structured data document system having a duplicated tree structure includes a map store (350, 352). A map index (354) has a map pointer pointing to a location in the map store in one of the map index's locations. A duplicate array (364) contains a second map pointer. The map index (354) has an array pointer that points to the duplicate array. The duplicate array stores map pointers pointing to duplicates of tags or data stored in the map store.