Convert Terrain trees in to real trees

Hi I want to convert the trees painted on the terrain in to actual instances of the tree models. I've found TerrainData.treeInstances in the docs, but there's no info on functionality. I can find the position of a tree in the treeInstance struct, but how do I... 1) know which of the 5 tree-types I'm using a particular terrain-tree is? 2) after instantiating a real one, how do I delete the one in the terrainData?

Thanks