The book explains the use of Trees in Logic, in particular Propositional, Predicate, Identity, and Modal Trees. The book contains 24 interactive 'widgets' which the User or Reader can use to do interactive exercises or construct trees of their own. Most of these just require gestures with fingers, such as tapping or swiping. But many of the widgets will accept typed, or pasted, input. The book also contains about forty diagrams and images, and two videos.