refactored Tree implementations to be es6 classes
refactored Tree implementations to be es6 classes

antlr/antlr4,parrt/antlr4,parrt/antlr4,antlr/antlr4,antlr/antlr4,parrt/antlr4,parrt/antlr4,parrt/antlr4,antlr/antlr4,ericvergnaud/antlr4,parrt/antlr4,ericvergnaud/antlr4,parrt/antlr4,ericvergnaud/antlr4,antlr/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,antlr/antlr4,ericvergnaud/antlr4,parrt/antlr4,ericvergnaud/antlr4,parrt/antlr4,antlr/antlr4,antlr/antlr4,antlr/antlr4,ericvergnaud/antlr4,parrt/antlr4,ericvergnaud/antlr4,antlr/antlr4