The Simple Tree Generator is a small project in Unity which you can generate trees with.
They can be generated in the editor or at runtime.
The first part of the tree generation is the growth of a graph. A graph is a set of nodes and each node has a length, a direction and a thickness. According to the tweakable options and randomness a new node grows from the end of the last node. There is also a chance for a split, creating a new branch. Most trees that I have observed in nature don't decrease gradually in diameter but rather split their surface area between the split trunks. As such this is how I choose to implement it as well. After a split, the node length is decreased as well.
Each trunk generates a mesh by adding circular structures of vertices with nodes at its center. In order to decrease the amount of generated vertices, a new set of vertices is only created when the curvature of the growth exceeds a certain value. This, as well as the density of vertices for a circular structure, is adjustable in the settings.
My main focus in this project was the mesh generation of the trunks as well as using no extra resources like textures. Thats why I chose to simply generate a leaf with Unity`s AnimationCurve class. In the leaf settings you can set a few points to generate one half of the outline of the leaf. This information is mirrored for the whole leaf as such a texture with adjustable resolution is generated. Each pixel is basically only holding information if its part of the leaf or not. The mesh of the leaf is a set of 2 triangles each containing 3 vertices. All leaves are part of the same mesh with a shared material to optimize performance.