Will it be possible to expose the Element position property for the treeview in the object inspector. I had to really scratch my head to get it fit in a div and finally found out   WebTreeView1.ElementPosition := epignore; did the trick.

Secondly the tree view comes with its own css and class names for each of the ul and li elements. How do I override the class names and classes use my own css instead ?

There is at this moment not a property exposed for this.
This is a good suggestion, we'll investigate to add this for a future update.

there is a sample how to format WebTreeView with standard css bootstrap lib ? like used in sample

We do not have this demonstrated in an included sample at this moment.
In the TWebTreeView, you have 3 CSS classes:

ElementClassName : class for treeview outer DIV
ElementNodeClassName: class for node in normal state
ElementNodeSelectedClassName: class for node in selected state