Tree cement

When my uncles and aunts were visiting me in June, my uncle Curt suggested I put cement in a rotting part of my willow tree.  Years ago there were a few more major tree trunks sections in the willow tree and dad cut them off.  Over the years one of the cut trunks rotted and insects got into it.   My uncle suggested I dig out the loose rotted stuff, then spray the hole with an insect killer, then seal the hole with cement.

I did as he suggested.  This was all the cement I had. I used 90 lbs of cement.  It did not reach the top.  The slope of the cement is steeper than it looks.  I am undecided whether to buy another bag of cement and try to make the cement plug reach the top of the stump, or use whatever (I forgot what it is) my uncle told me to use to seal the cracks in the rest of the stump.