protected AssemblyProduction getRootRecursion() {
		assert tree.getParent() == null;
		AssemblyProduction rootProd = tree.getProduction();
		AssemblyNonTerminal start = rootProd.getLHS();
		AssemblyProduction rec = grammar.getPureRecursion(start);
		return rec;
	}
If applicable, get the {@code I => I} production of the grammar

@return the production
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/app/plugin/assembler/sleigh/sem/AbstractAssemblyTreeResolver.java