https://blendermarket.com/products/alpha-trees

  3D tree models are slow  Traditional tree models often have millions of polygons, and multiple complex materials, making them very slow to render. They also slow down the viewport and add to visual noise while working.  They also use a lot of memory  Another problem with having all of those polygons and textures is that they can add up and overload the memory limits of your GPU, resulting in having to render on the CPU, which is often 5 to 10x slower.