Hi Serdar,
Thanks for your interest in Syncfusion products.
On click of the Treeview node the link can be displayed in new tab by setting NavigateUrl and target property to the nodes and also please change Internet Explorer settings as mentioned below.
1.Open Internet Explorer.
2.Click the Tools button,and then click Internet Options.
3.Click the General tab, and then, under Tabs, click Settings.
4.In the Tabbed Browsing Settings dialog box, do the following:
•Select the radiobutton "Always open pop-ups in a new tab" under "When a pop-up is encountered".click OK, and then click OK again.
Please refer to the sample provided in the below link.
http://files.syncfusion.com/samples/Tools.Web/7.3.0.20/Forum_90794/Main.htmWork on the sample and let me know Whether your query is solved.
Regards,
Kamala Archana