You'll probably want to stake it for support.

The graft union--if there is one on mulberry--is always above the ground. You plant at or below (raised bed) the root flare on all fruit/nut trees except pecan (2" below shows increased survival which is why they come painted to mark the level where to bury them).

The graft union can be above or below ground depending on whether you want the scion to grow it's own roots or not over time.
The best thing you could do for that weak graft union is plant it deeply and stake it.