Find the Alpha Trees panel in the N-panel in the 3D view.
Add a new biome slot by clicking the "+" button next to the biome list.
Add some new biome settings by clicking the "New biome settings" button
Change the scattering settings to your liking. Settings like density and scale are especially important
Add a new tree by clicking the "+" button next to the tree list.
Select a tree you like from the library by clicking on the default tree icon.
Repeat 5 and 6 until you have enough trees for this biome. Generally, it's best to stick to one species per biome.
Repeat all steps to build up a realistic forest!
For more info about scattering, see Biomes
Tips and Tricks
Have a question about part of the addon? On most panels, there are info panels that will tell you about a certain feature and it's uses.
You can copy almost any setting to another biome, tree or object. Just click the little copy icon to open a dialogue that allows you to choose what settings to copy, and what to copy them to.
If you want to edit the Alpha Trees settings for a single object, even when you select a different one, you can click the pin button to pin the current object.
If it's difficult to find the tree you're looking for, you can filter the shown trees using the search dropdown, and filter by type, species and variant.
You can add multiple trees at once using the multi import button, both for single trees and for particle trees.
You can hold hotkeys while toggling the visibility of list items to change which items it affects:
Shift to toggle all items on or off
Ctrl to invert all items
Ctrl + Shift to isolate the selected item
Still running out of memory in large scenes? Lowering the quality of a tree is a good way to reduce memory use of the tree, and often it can't be noticed in a final render. Low quality uses 64x less memory than high quality.
If you want to use a biome or collection of biomes in multiple files, you can export biomes to JSON files, which can then be imported again.
If you have multiple cameras in your scene, you can enable "use scene camera" mode, which will mean that trees will automatically face the active camera, and camera clipping will also apply to the active camera