To make the public API consistent with other acts_as libraries, such as acts_as_list.
Let railtie autoload ActiveRecord::Acts::Tree
@kenn Thanks for the pull request.
I intentionally made the change to acts_as_tree to force uses to explicitly include the module in the models they want that support in. Rails 4 will no longer have the init.rb hook that previous versions did. You can see an example in the README.
I will merge this in for consistency purposes, but I expect that in a future change I'll force users to use the module. Thanks again for your help!
@kenn The new version is live: https://rubygems.org/gems/acts_as_tree/versions/1.0.1