organic chemistry - Is the index 1 in the substituent name "1-methylethyl" a redundant index?

I want to identify the correct IUPAC name for this compound:

I would say this is 2-methyl-5-(methylethyl)-5-(1-methylpropyl)-nonane. However, the solution manual says that it is 2-methyl-5-(1-methylethyl)-5-(1-methylpropyl)-nonane.

I don't understand why the first "1-" index is necessary. It doesn't add any information, as "(2-methylethyl)" would actually be just a propyl.

Am I missing something?