cut another inch off the top, put some cross cuts into it then add a stump and rook killer [In the UK we have SBK]. Paint the chemical on according to instructions and usually cover with plastic/bucket to keep animals off it. The poison then goes down into the roots.

I do exactly that works every time just left with stumps for years.

Thanks for the suggestions. I'll give it a go. The wood is so dense, it burned out the motor on my chainsaw. The replacement is bigger, but it's being pushed to the max. I'm so happy to see this tree go.

You can drill holes if the wood is too hard to score and pour solution into them