Open View → Behaviour Tree Editor (shown below) to launch the OpenCAGE Behaviour Tree Editor. Unlike the other editors under View, this runs as a separate process (a Brainiac Designer fork with OpenCAGE's LegendPlugin node set) and works on global AI data — you don't need a level loaded.
Authoritative trees live in:
DATA/BINARY_BEHAVIOR/_DIRECTORY_CONTENTS.BML — packed catalogue the game loadsOn startup the editor extracts every tree to DATA/BEHAVIOR/*.xml for editing (it clears existing XMLs first) and lists them under Behaviours in the Explorer, as shown below. That folder is scratch space — don't treat leftover XMLs as a permanent source of truth.
Nothing is open yet: the palette groups under the tree list start collapsed, and the document area and Properties panel stay empty until you open a tree.
Closing OpenCAGE, or choosing View → Behaviour Tree Editor again, kills any open Behaviour Tree Editor instance without prompting. Save first if you have unsaved graphs.
The main layout:
Double-click a tree in Explorer to open it as a document tab, as shown below. Drag nodes from the palette onto the canvas and wire the graph; select a node to edit its properties in the Properties panel (Show Properties, next to Save, pops the selected node's properties out into a floating panel). Left-drag the background to pan and scroll to zoom when a graph runs off the canvas, as it does here. The ? button in the window's top-right corner opens the Behaviour Tree Nodes reference.
alien_flamed_unaware open in a document tab with its Sequence node selected; the node's parameters appear in the Properties panel on the right.
You can also export a graph snapshot with the Save Image Of Behavior button, the rightmost of the three in the canvas's top-right corner (the dialog is titled Save Graph As Image; *.emf or *.png). This editor does not edit per-level WORLD/BEHAVIOR_TREE.DB files.
Shortcuts depend on focus — graph canvas vs Explorer. There is no Ctrl+S save shortcut; use the Save button in the top-right corner of the open tree's canvas (its tooltip reads Save Behavior). The same list of controls is available in OpenCAGE under Options → Controls, on the Behaviour Tree Controls tab.
When the behaviour graph has focus:
Copy / cut / delete apply to non-root nodes only. There is no undo/redo on the canvas.
When the Explorer tree list has focus:
Explorer does not use Ctrl+C / Ctrl+V / Ctrl+X, and there is no button for creating a brand-new tree — the shipped catalogue is edited, renamed (F2) or deleted in place. Delete here removes trees from the catalogue, not nodes from an open graph.
Use the Save button at the top-right of the tree's canvas (shown below) — not OpenCAGE's File → Save Level. Save writes XML for the tree(s), then repackages all DATA/BEHAVIOR/*.xml files back into _DIRECTORY_CONTENTS.BML.
Each open tree has its own Save button at the top-right of its canvas; beside it are Show Properties and Save Image Of Behavior.
If you close the editor's window with unsaved graphs, the Unsaved Behaviors dialog lists them with checkboxes and offers Save Selected Behaviors, Discard All Unsaved Changes, or Cancel.
Editing a tree changes the global definition. To point a character at a tree name from that catalogue, use View → Configuration Editors → Characters → Attributes and the Behaviour Tree field (names come from _DIRECTORY_CONTENTS.BML).
To restore stock trees, open the Backup Manager → Revert Configs → Reset Behaviour Trees. That closes the game and Behaviour Tree Editor if open, restores the vanilla BML, and refreshes the DATA/BEHAVIOR extract.