Is it possible to use same item look for more than one treeview?

Yes. You can use same item look for all the treeviews by creating ItemLooks instance programmatically and these ItemLooks can be applied to the treeview items like below.

C#

TreeViewItemLook look = new TreeViewItemLook();

look.StateDataDefault.ItemCSSClass = "Def_ItemCss";

look.StateDataExpanded.ItemCSSClass = "Exp_ItemCss";

look.StateDataHover.ItemCSSClass = "Hov_ItemCss";

look.Enabled = false;

 //Add to treeview1

TreeView1.ItemLooks.Add(look);

 //Add to treeview2

TreeView2.ItemLooks.Add(look);

 //Add to treeview3

TreeView3.ItemLooks.Add(look);

VB

Dim look As TreeViewItemLook = New TreeViewItemLook()

look.StateDataDefault.ItemCSSClass = "Def_ItemCss"

look.StateDataExpanded.ItemCSSClass = "Exp_ItemCss"

look.StateDataHover.ItemCSSClass = "Hov_ItemCss"

look.Enabled = False

''Add to treeview1

TreeView1.ItemLooks.Add(look)

''Add to treeview2

TreeView2.ItemLooks.Add(look)

''Add to treeview3

TreeView3.ItemLooks.Add(look)

Please refer the sample in the below link which illustrates the above:

http://websamples.syncfusion.com/samples/Tools.Web/5.2.0.25/Treeview/main.htm