For the following messages, node stands for a tree node or a reference to one and root stands for a tree box or a reference to one.
Caution: If you send a root node that contains one or more nodes with the Set Node Select Script defining a collapse message, then Mac runs the script twice. Windows doesn’t run the script. This behavior on Macintosh doesn’t just affect increments. Any script runs twice. It will print to the log twice, create a column twice, try to delete something twice, and so on.
Table 2.1 shows the results for a Tree Box() that contains the MultiSelect argument.
Returns 1 for a MultiSelect tree and 0 for a single-select tree.
Selects the given tree node in the tree display box. In list of tree nodes, all nodes in the list are selected for MultiSelect trees. Otherwise, the first node in the list is selected. Specify the Boolean argument to indicate whether the node or nodes should be selected or unselected. The default value is 1, which selects the nodes.
Notes: 
On Windows, the <<Set Selected() message expands all nodes between the selected node or nodes and the root of the tree; items that are selected deep within the tree are shown. The expansion state does not change for nodes that were previously selected.
On Macintosh, <<Set Selected() does not change the tree expansion state.

Help created on 10/11/2018