The graphic recursiveDescentParser.jpg helps in understanding the recursive calls. The parser does not build a visible tree. It builds a string considering the grammar.
5+6*7 becomes 6*7+5
Due to the conversion of the term, the parser rather falls into the category of 'term rewriting'.
In its prototype version, the parser is only able to handle single-digit numbers and operators (+,-,/,*). If other characters are entered, the application cannot handle them.