Demo: tweak TreeNode demo.

imgui_demo.cpp

@@ -901,13 +901,18 @@ static void ShowDemoWindowWidgets()
                 if (i == 0)
                     ImGui::SetNextItemOpen(true, ImGuiCond_Once);
 
-                if (ImGui::TreeNode((void*)(intptr_t)i, "Child %d", i))
+                // Here we use PushID() to generate a unique base ID, and then the "" used as TreeNode id won't conflict.
+                // An alternative to using 'PushID() + TreeNode("", ...)' to generate a unique ID is to use 'TreeNode((void*)(intptr_t)i, ...)',
+                // aka generate a dummy pointer-sized value to be hashed. The demo below uses that technique. Both are fine.
+                ImGui::PushID(i);
+                if (ImGui::TreeNode("", "Child %d", i))
                 {
                     ImGui::Text("blah blah");
                     ImGui::SameLine();
                     if (ImGui::SmallButton("button")) {}
                     ImGui::TreePop();
                 }
+                ImGui::PopID();
             }
             ImGui::TreePop();
         }