Why tree's items are displayed like a pointer in MVVM?

            <tree model="@load(vm.definitions)" selectedItem="@bind(vm.selected)" checkmark="true">
                <treecols visible="false">
                    <treecol label="" />
                </treecols>
                <treechildren>
                    <template name="model" var="definition">
			<treeitem>
                            <treerow>
                                <treecell label="@load(definition.name)" />
                            </treerow>                        
                        </treeitem>
                    </template>
                </treechildren>
            </tree>

    private TreeModelDefinition definitions;

public class TreeModelDefinition extends AbstractTreeModel<Definition> {

        public boolean isLeaf(Definition e) {
          ...
        }

        public Definition getChild(Definition e, int i) {
            ....
        }

        public int getChildCount(Definition e) {
            ...
        }
}