indentation property
The number of pixels children will be offset by in the cross axis based on their TreeViewNode.depth.
By default, the indentation is handled by RenderTreeViewport. Child nodes are offset by the indentation specified by TreeViewIndentationType.value in the cross axis of the viewport. This means the space allotted to the indentation will not be part of the space made available to the Widget returned by TreeView.treeNodeBuilder.
Alternatively, the indentation can be implemented in TreeView.treeNodeBuilder. By providing TreeViewIndentationType.none, the depth of the given tree row can be accessed in TreeView.treeNodeBuilder through TreeViewNode.depth. This allows for more customization in building tree rows, such as filling the indented area with decorations or ink effects.
Implementation
final TreeViewIndentationType indentation;