The Scene tree window and the Node Attribute panel works interactively with two attributes - Selected and Included.
Selected - When you click the name of the node, it will also be shown in the Selected box of the node attribute. See Selecting Mesh Nodes for more details.
Included - You can see that each node has one check box in front of its name. When the box is check, 3DXchange includes this node in exporting process. This function facilitates you to export certain objects in a scene as one single object. See Including and Excluding Mesh Nodes for more details.