Insertion point in a richtextbox

[sympatico]

I'm developing a program that allows the user to click a button to input an
html tag into a text document. What I'm having trouble finding is how to
insert the text at the insertion point instead of at the end of the document
I'm currently using
rtbCode.Text = rtbCode.Text & "INSERT TEXT"

for the button click event.

Thanks in advance.