Added the MPExpressionTree Classes

MathPad/MPParenthesisFunctionLayout.m

@@ -154,6 +154,12 @@
     return bounds;
 }
 
+#warning Let the children be drawn automatically
+- (BOOL)drawsChildrenManually
+{
+    return YES;
+}
+
 - (void)draw
 {
     NSBezierPath *openingParens = self.transformedOpeningParens;