Structure of tree view table fields
A tree view table field can obtain data from only one form, either local or remote. Each level of a tree view table represents a field from the source form (or a column in a list view table). Each node represents one or more requests from that form. Ideally, each leaf node should contain data from a field in one request.
For example, the tree view table in the following figure has these levels:
Example tree view table levels
Example of tree levels, nodes, and leafs
(Click the image to expand it.) 
You use the Sort/Levels property of the tree view table field to specify which fields from the source form appear as levels in the tree view (see Setting sort order and visible levels). You cannot use the following fields as tree levels:
- Attachment fields, diary fields, or character fields with a data length of more than 255 bytes.
- Display-only fields
Tree levels are also fields, and you can specify their properties.
For more information, see Creating table fields.