just pot it into damp media .....

why in teh world would you put it in water???

and you should have potted it when that root was less that in inch long.. dont wait any longer than you have too ...

pot it up ...

you are near loving it to death .. its a tree .. grow it like a tree ... its not some rare baby that needs this delicate care ... nor is it an aquatic.. that lives in water ...

and growing it like a tree.. means using a media that is friendly to trees .... very generally.. trees like a sip of water... and near total drainage ...

can you get that kind of media ... if not.. a cactus mix with a little extra peat will work ...

mother earth in a pot... usually will not work ...

ken

https://duckduckgo.com/?q=potting+Mango+Seed&t=ffcm&iax=videos&ia=videos

I agree. Starting the seedling in water will cause it to grow roots full of spongy material called aerenchyma. The open porosity of aerenchymous tissue allows the plant to get the oxygen it needs to drive root function from above the waterline via diffusion through the airy tissue. When you try to transplant water roots into soil, the roots will handle the transition poorly with many highly prone to breaking or simply dying. It would be much better to A) use a VERY sharp tool to trim the taproot back to where you see the fine roots immediately below the cotyledons and lay it on top of a damp and very well-aerated medium. B) cover with about 1/4" of peat or potting soil and mist the soil enough to make it damp. Continue misting for a few days - just enough to keep the top of the soil damp - you don't want to mist so heavily you saturate the soil beneath the seedling. By following those steps, you'll ensure the roots come on line able to function normally in a solid medium and (by trimming the taproot) they will be well-branched, which will make any future work you do on the roots MUCH easier.

Al