Identifies the handle of a loaded bitmap, so that images from that bitmap can be shown in items in the tree view. You obtain the bitmap handle by calling the library routine W$BITMAP with the WBITMAP-LOAD option. The bitmap is treated as a bitmap strip — a series of fixed-width images laid out side-by-side in a single bitmap. The images are numbered sequentially, starting at 1. Note that you have only one bitmap strip for the entire control, although you can select individual images out of this strip for each item. See BITMAP-NUMBER.