lesscss version of bootstrap3 dropdown submenu solution (shown on mouse-over). css-version: http://firdaus.grandexa.com/2013/09/twitter-bootstrap-3-multilevel-dropdown-menu/

dropdowns.less

/* css hover version of .dropdown */
.dropdown-hover {
    .dropdown ();
    &:hover {
        > .dropdown-menu {
            display: block;
        }
    }
}

/* new dropdown-submenu (css hover version) */
.dropdown-submenu-hover {
    .dropdown ();
    position:relative;
    > .dropdown-menu
    {
        top:0;
        left:100%;
        margin-top:-6px;
        margin-left:-1px;
        -webkit-border-radius:0 6px 6px 6px;
        -moz-border-radius:0 6px 6px 6px;
        border-radius:0 6px 6px 6px;
    }
     
    > a:after {
        display:block;
        content:" ";
        float: right;
        width:0;
        height:0;
        border-color:transparent;
        border-style:solid;
        border-width:5px 0 5px 5px;
        border-left-color: @dropdown-caret-color;
        margin-top:5px;
        margin-right:-10px;
    }
     
    &:hover {
        background-color: @dropdown-link-hover-bg;
        
        > .dropdown-menu {
            display:block;
        }
        > a {
            color: @dropdown-link-hover-color;
            &:after {
                border-left-color: @dropdown-caret-hover-color;
            }
        }

    }
     
    .pull-left {
        float:none;
        > .dropdown-menu {
            left:-100%;
            margin-left:10px;
            -webkit-border-radius:6px 0 6px 6px;
            -moz-border-radius:6px 0 6px 6px;
            border-radius:6px 0 6px 6px;
        }
    }
}