selenium.click("//*[@id='ext-gen15']/li/div/img[1]");

selenium.click("//*[@id='ext-gen15']/li/ul/li[1]/div/img[1]");

/html/body/div[1]/div/div/ul/li/div/img[1];
//html/body/div[1]/div/div/ul/li/ul/li[1]/div/img[1];
//html/body/div[1]/div/div/ul/li/ul/li[2]/div/img[1];
//html/body/div[1]/div/div/ul/li/ul/li[2]/ul/li/div/img[1];
//html/body/div[1]/div/div/ul/li/ul/li[2]/ul/li/ul/li/div/img[1];
//html/body/div[1]/div/div/ul/li/ul/li[3]/div/img[1];
//html/body/div[1]/div/div/ul/li/ul/li[3]/ul/li/div/img[1];
//html/body/div[1]/div/div/ul/li/ul/li[4]/div/img[1];

//img[@class='x-tree-ec-icon x-tree-elbow-plus']

//img[@class='x-tree-ec-icon x-tree-elbow-plus'][1]