也就会显示加号了，等展开节点a时，再把刚才默认创建的子节点b移除就能够了，删除方法是先推断展开的节...
b4-collapse-accordion Collapse accordion b4-collapse-button Collapse button b4-collapse-default Collapse default Dropdown 下拉 TriggerDescription b4-dropdown-alignment Dropdown alignment b4-dropdown-anchor Dropdown anchor b4-dropdown-button Dropdown button b4-dropdown-colored Dropdown colored b4-dropdown...
file-code file-edit file-excel file-exclamation file-image file-minus file-pdf file-plus file-powerpoint file-times file-video file-word film film-alt filter fire fire-extinguisher flag flag-checkered flask folder folder-open font football-ball football-helmet forward frown futbol gamepad gavel gem...
b4-collapse-accordion Collapse accordion b4-collapse-button Collapse button b4-collapse-default Collapse default Dropdown TriggerDescription b4-dropdown-alignment Dropdown alignment b4-dropdown-anchor Dropdown anchor b4-dropdown-button Dropdown button b4-dropdown-colored Dropdown colored b4-dropdown-defau...