In essence, the tree method is a casework approach and very intuitive. In a probability tree:
To find the answer, we work from leaves towards root by:
The tutorial video gives a visualized example of the above mentioned rules.
(2732) A bug crawls from $A$ along a grid. It never goes backward, it crawls towards all the other possible directions with equal probability. For example:
The questions are, from $A$:
