Expressions and precedence in AST

When it comes to expressions, the higher priority items are being called by lower priotrity items. So, higher priority items reside in leaf level of the AST and they get executed first. Once all the sub trees get executed, parent trees will execute. First, ANTLR will look for the lowest priority item, which is in the top level and then it executes the higher priority item which is down the line, the following a top-down parsing strategy.