The left-hand side of 保 means “person” but refers in this case to a mother or nursemaid. The right-hand side evolved from a form that resembled a hung man in Hangman. That shape represented a child thoroughly wrapped in a blanket. Henshall says (in his telegraphic style), “Wrapped child later became graphically confused with tree/wood 木.” I know he means that the symbol of the wrapped child became confused with the symbol of a tree. But it’s more fun to read it as being about the mother who mistook her baby for a tree!
