minecraft-bedrock-json-schemas/source/behavior/features/growing_plant.md

UP and DOWN can be lowercase or uppercase.
Head and body blocks must be arrays of arrays (see my code).
The first value of an array in the height distribution array or the value of the "age" property may be of the form {"range_min": 1, "range_max": 13} or an integer. In other words, the schema is terrible with this one. Again, see my code.