You have an account on AiGameDev.com, but it looks like you have not yet signed up as an INSIDER (free). It’s a one click process, see below:
In this presentation, Alex Champandard talks about using behavior trees to create responsive yet purposeful decision-making and control systems. In particular, you'll learn how behavior trees combine the best features of linear scripts and reactive state machines, yet provide the goal-directedness of planners. You'll learn about the structure of behavior trees and what you need to implement them, as well as useful patterns for designing scalable AI logic based on them.