You can make buttons open any web page - not just nodes in your own tree. The trick is to have the button open a Link Node.

Create a Link Node as follows:

1. Click + New Node or add an action button to a current node that connects to a new node.
2. Select Link Node as the node type.
3. Enter the URL to link to. Direct Link is set by default, as this will avoid pop-up blockers.
4. You can also choose to Open Link in a New Tab.
5. Make sure that you've connected an action button to the new Link Node.

Editing a link node looks like this:

When your users click a button that is connected to a link node, they get redirected to the URL you specified. Plus, this action is tracked as a part of their Zingtree session.