recover deleted child in firebase realtime database android

I need some help to undo deleted child, I already have the snackbar showing the undo onclick but I am not sure how to recover the child, I have it saved in ExpenseBackUp, but how do I get it back? any idea?

    delete.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("Expenses").child(FirebaseAuth.getInstance().getCurrentUser().getUid());
            reference.child(postId).removeValue().addOnCompleteListener(new OnCompleteListener<Void>() {


                Expense expenseBackUp = new Expense(item, category, date, postId, amount);

                @Override
                public void onComplete(@NonNull Task<Void> task) {


                    if (task.isSuccessful()) {
                        Snackbar.make(rv, item + " has been deleted", Snackbar.LENGTH_LONG).setAction("UNDO", new View.OnClickListener() {
                            @Override
                            public void onClick(View view) {
                                //undo onClick actions
                                
                                Toast.makeText(ExpensesActivity.this, item+" recovered", Toast.LENGTH_SHORT).show();
                            }
                        }).show();

                    } else {
                        Toast.makeText(ExpensesActivity.this, "Something went wrong, try again" + task.getException(), Toast.LENGTH_SHORT).show();
                    }

>Solution :

Are you looking for:

reference.child(postId).setValue(expenseBackUp)