Having end node pointer would be helpful for removing the end node of graph.

To be safe, set max number of item size to Number.MAX_SAFE_INTEGER (9,007,199,254,740,991)

The graph that is holding bigger than 9,007,199,254,740,991 would be very huge data.

So by the size, bigger than 9,007,199,254,740,991 items wouldn't work in current regular hardwares.

For insertion operation:

this.start;
this.end;

end node ref does not get updated.

Insertion of 4 create wrong structure of Btree.
If that's the case, this might be happening in all other even number of order.

This is happening because the bgraph is spliting root wrong when the order is even number.

Fix by:

if(listNode === undefined) break;