I would assume you couldn’t get the entire mesh into roblox perfectly following the triangles limit, however I’m pretty sure people take the texture from the blend and create a decal and post it onto an invisible part. I’ve never worked with realistic trees though, so I couldn’t tell you exactly.
Hi, try setting the transparency value of the leaf mesh to 0.02 or as low as you can, to make the part disappear, and the texture appears with no background (part).
Both methods work perfectly fine, the separate planes work as well as the hair particles; the hair particles are placing those planes automatically (and depending on settings, randomly) around the mesh.
I used separate planes for the branches so I can have control over the shape of the tree. Though using hair particles works fine, I do not recommend sticking to that method since the control over the shape is very limited. Additionally, it promotes laziness which equates to low quality work.
The best way of building a realistic game-ready tree is to build from top to down: starting from the leaves down to the trunk. Sculpt the leaves or alternatively get a leaf texture reference. Add the leaves to a branch then bake them into a plane. This is to reduce the triangle count so the game can run smoothly. Cut out the plane and shape it to add depth. Finally, create the trunk then add the branches. I hope that you get the idea.