Download 35 tree models in FBX format

[René]

I haven't tested these; I don't even know how to import properly as FBX (never tried). Note, however, that the hi-res versions are not free.

http://www.cgchannel.com/2020/11/download-15-free-hi-res-tree-models-in-fbx-format/

[cyphyr]

Good find.
Terragen will not import FBX models (yet). You'll have to convert the files to obj in your favourite modelling package.

[René]

Ah, good to know. Thank you.

[WAS]

Thanks for sharing! No textures makes it a little hard to work with for some but still probably useful. 

Blender does a straight forward import and export if you don't have something else better.