Thank you for contacting Syncfusion support.
We would like to inform you that you can achieve your requirement by adding a SearchBar inside any Views such as StackLayout or GridLayout over the SfTreeView control. We have attached a sample for your reference. Please find the sample from the below link.
Note: TreeView doesn't support filtering. So, you have to manually filter the underlying data based on your requirement.
Please let us know if you have any queries.