There are some guidelines you have to follow to do an import into OSM: https://wiki.openstreetmap.org/wiki/Import

  1. is license compatible
  2. describe how you want to do your import on the wiki, make sure you do not create duplicates
  3. get support for your import in the local community
  4. check with the import mailing list if everything is OK
  5. go ahead.

There have been imports of trees in the past. Lot’s of trees have been mapped by hand as well.