Enables the tree to track when it is changing.
Call GTree.TGCustomTree.BeginUpdate before directly modifying the tree (adding or deleting nodes), and GTree.TGCustomTree.EndUpdate after. When implementing properties or methods that change the tree in descendants of the tree, call BeginUpdate before the changes are made, and EndUpdate when the changes are complete.
The BeginUpdate method may be nested inside other BeginUpdate method calls. The first call to BeginUpdate will fire an OnChanging event. The tree will not fire an GTree.TGCustomTree.OnChange event until an equal number of EndUpdate method calls are made. Therefore, always ensure you protect the calling of the EndUpdate method call in a try-finally block.