How do I validate treeview node in VB.NET?

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VB

I have a treeview control on a page. And some nodes have an pdf file and some are not having the same. I want to display only those nodes are having pdf files and rest of others should be hide. Then what will be the process?

What I have tried:

<asp:TreeNode Text="Medical" Value="Medical" SelectAction="None">
<asp:TreeNode Text="Anaesthesia" Value="New Node" NavigateUrl="~/Catalogue/Medical/Anesthesia 2016.pdf" Target="_blank">
<asp:TreeNode Text="Anatomy" Value="New Node" NavigateUrl="~/Catalogue/Medical/Anatomy 2016.pdf" Target="_blank">
<asp:TreeNode Text="Biochemistry" Value="New Node" NavigateUrl="~/Catalogue/Medical/Biochemistry 2016.pdf" Target="_blank">
<asp:TreeNode Text="Cardiology and ECG" Value="Cardiology and ECG" NavigateUrl="~/Catalogue/Medical/Cardiology ECG 2016.pdf" Target="_blank">
<asp:TreeNode Text="Community Medicine" Value="Community Medicine" NavigateUrl="#">
<asp:TreeNode Text="Dermatology" Value="Dermatology" NavigateUrl="~/Catalogue/Medical/Dermatology 2016.pdf" Target="_blank">
<asp:TreeNode Text="Ear, Nose and Throat" Value="Ear, Nose and Throat" NavigateUrl="#">
<asp:TreeNode Text="Forensic Medicine and Toxicology" Value="Forensic Medicine and Toxicology" NavigateUrl="~/Catalogue/Medical/Forensic Medicine Toxicology 2016.pdf" Target="_blank">
<asp:TreeNode Text="Gastroenterology" Value="Gastroenterology" NavigateUrl="~/Catalogue/Medical/Gastroentereology and Hepatology 2016.pdf" Target="_blank">
<asp:TreeNode Text="Instruments" Value="Instruments" NavigateUrl="#">
<asp:TreeNode Text="Medical Laboratory Technology" Value="Medical Laboratory Technology" NavigateUrl="#">
<asp:TreeNode Text="Medical Statistics" Value="Medical Statistics" NavigateUrl="#">
<asp:TreeNode Text="Medicine" Value="Medicine" NavigateUrl="#">
<asp:TreeNode Text="Microbiology" Value="Microbiology" NavigateUrl="~/Catalogue/Medical/Microbiology, Immunology & Parasitology 2016.pdf" Target="_blank">
<asp:TreeNode Text="Neurology" Value="Neurology" NavigateUrl="~/Catalogue/Medical/Neurology & Neurosurgery 2016.pdf" Target="_blank">
<asp:TreeNode Text="Obstetrics and Gynaecology" Value="Obstetrics and Gynaecology" NavigateUrl="#">
<asp:TreeNode Text="Oncology" Value="Oncology" NavigateUrl="~/Catalogue/Medical/Oncology 2016.pdf" Target="_blank">
<asp:TreeNode Text="Ophthalmology" Value="Ophthalmology" NavigateUrl="~/Catalogue/Medical/Ophthalmology 2016.pdf" Target="_blank">
<asp:TreeNode Text="Orthopaedics" Value="Orthopaedics" NavigateUrl="~/Catalogue/Medical/Orthopedics 2016.pdf" Target="_blank">
<asp:TreeNode Text="Paediatrics" Value="Paediatrics" NavigateUrl="~/Catalogue/Medical/Pediatric 2016.pdf" Target="_blank">
<asp:TreeNode Text="Preventive and Social Medicine" Value="Preventive and Social Medicine" NavigateUrl="#">
<asp:TreeNode Text="Psychiatry" Value="Psychiatry" NavigateUrl="#">
<asp:TreeNode Text="Parasitology" Value="Parasitology" NavigateUrl="#">
<asp:TreeNode Text="Pathology" Value="Pathology" NavigateUrl="~/Catalogue/Medical/Pathology & Hematology 2016.pdf" Target="_blank">
<asp:TreeNode Text="Pharmacology" Value="Pharmacology" NavigateUrl="#">
<asp:TreeNode Text="Physiology" Value="Physiology" NavigateUrl="~/Catalogue/Medical/Physiology 2016.pdf" Target="_blank">
<asp:TreeNode Text="Radiology" Value="Radiology" NavigateUrl="#">
<asp:TreeNode Text="Surgery" Value="Surgery" NavigateUrl="~/Catalogue/Medical/Surgery 2016.pdf" Target="_blank">
<asp:TreeNode Text="Urology" Value="Urology" NavigateUrl="~/Catalogue/Medical/Urology 2016.pdf" Target="_blank">
<asp:TreeNode Text="Dictionary" Value="Dictionary" NavigateUrl="#">
<asp:TreeNode Text="Differential Diagnosis" Value="Differential Diagnosis" NavigateUrl="#">
<asp:TreeNode Text="FAQs" Value="FAQs" NavigateUrl="#">
<asp:TreeNode Text="Jaypee Gold Standard Mini Atlas Series" Value="Jaypee Gold Standard Mini Atlas Series" NavigateUrl="#">
<asp:TreeNode Text="Jaypee Video Atlas Series" Value="Jaypee Video Atlas Series" NavigateUrl="#">
<asp:TreeNode Text="MCQs and Self Assessment Series" Value="MCQs and Self Assessment Series" NavigateUrl="#">
<asp:TreeNode Text="Other Useful Books" Value="Other Useful Books" NavigateUrl="#">
<asp:TreeNode Text="PLAB" Value="PLAB" NavigateUrl="#">
<asp:TreeNode Text="Step by Step Series" Value="Step by Step Series" NavigateUrl="#">
<asp:TreeNode Text="Viva Voce" Value="Viva Voce" NavigateUrl="#">