Also you will want to stump the tree and graft onto new growth if you have a tree that is already growing well and you hang a 2nd type on it, the new type will most likely never catch up to the original tree. That is assuming you want them to be equal halves.
That is reworking / Topworking.
Any methods to produce double grafted trees from the seedling nursery stage ? i.e. as per Citrus or Stonefruit or Apple multi grafts ?
Clonal Avocado rootstocks sort of travel this path, until the lower stock is sacrificed.
Lots of people have one garden tree and need a pollinator.
Also wondering if I grafted high on a seedling rootstock, or already grafted nursery tree, would both sections throw fruiting branches after planting out ?
One of the members on the Citrus General Discussion top works Citrus high up, to keep part of the original variety fruiting, add a new variety and save tree space.