begin{landscape}
% Define block styles
tikzset{
desicion/.style={
    diamond,
    draw, thick,
    text width=4em,
    text badly centered,
    inner sep=0pt
},
block/.style={
    rectangle,
    draw, thick,
    text width=10em,
    text centered,
    rounded corners
},
cloud/.style={
    draw,
    ellipse,
    minimum height=2em
},
descr/.style={
    fill=white,
    inner sep=5pt
    },
connector/.style={
    -latex,
    font=scriptsize
},
rectangle connector/.style={
    connector,
    to path={(tikztostart) -- ++(#1,0pt) tikztonodes |- (tikztotarget) },
    pos=0.5
},
rectangle connector/.default=-2cm,
straight connector/.style={
    connector,
    to path=--(tikztotarget) tikztonodes
},
line/.style={>=latex,->,thick}
}


begin{figure}[htpb]
tikzset{font=large,
edge from parent fork down,
level distance=40pt,
edge from parent/.style=
    {draw=blue!50,
    thick
    },
filling/.style=
    {minimum height=12mm,
     draw=myfilling!75!black,
     very thick,
     drop shadow,
     rectangle,rounded corners,
     fill=myfilling,
    },
ntext/.style=
    {draw=none,
     text width=4cm,
     align=center
    },
}

centering
begin{tikzpicture}
begin{scope}[
every node/.style=
    {top color=white,
    bottom color=blue!25,
    rectangle,rounded corners,
    minimum height=8mm,
    draw=blue!25,
    very thick,
    drop shadow,
    align=center,
    text depth = 0pt
    },
]
Tree [.node (p) {Tank Overfill Event};
        [.node (o) {one};
            [.node (1) {one1};
                   [.node (11) {one11};
                        [.node (111) {one111};
                        [.node (a11) {one1111};
                            [.node (s) {ones};
                                    [.node (s1) {ones1};
                                        [.node (s11) {ones11};
                                              [.node (s111) {ones111};
                                                        [.ones1111
                                                              ]
                                                          ] ]
                                                       ]
                                                ]
                          [.twos
                             [.twos1
                                [.twos11
                                    [.twos111 node (s1111) {twos1111};] ] ]
                                        [.twos2 [.twos21
                                           [.twos211 node (s2111) {twos2111};] ]
                                             [.twos22 [.twos221 node (s2211) {twos2211}; ]
                                                           ] ]
                                                            ]
                                                            ]
                                                                ]
                                                              ] ]
                                                           ]
                                   ]
        [.node (two) {two};
            [.node (two1) {two1};
                  [.node (two11) {two11};
                  [.node (two111) {two111};
                     node (1111) {two1111};] ] ]
            [.node (two2) {two2};
                [.node (two21) {two21};
                  [.node (two211) {two211}; node (2111) {two2111};] ]
                   [.node (two22) {two22};
                    [.node (two221) {two221}; node (2211) {two2211}; ]
                            ] ] ]
         ]
end{scope}
% auxuliary constructs for level 4
node[left=of 111,ntext]
  (text4) {Level 4 text};
coordinate (aux2) at ([xshift=5pt]s2211.east|-text4);
% auxuliary constructs for level 3
node[ntext] at (text4|-11)
  (text3) {Level 3 text};
coordinate (aux4) at ([xshift=5pt]s2211.east|-11);
% auxuliary constructs for level 2
node[ntext] at (text4|-1)
  (text2) {Level 2 text};
coordinate (aux6) at ([xshift=5pt]s2211.east|-1);
% auxuliary constructs for level 1
node[ntext] at (text4|-o)
  (text1) {Level 1 text};
coordinate (aux8) at ([xshift=5pt]s2211.east|-o);
% auxuliary constructs for level 0
node[ntext] at (text4|-p)
  (text0) {Tank Overfill Event (A)};
coordinate (aux10) at ([xshift=5pt]s2211.east|-p);
% auxuliary constructs for level 5
node[ntext] at (text4|-a11)
  (text5) {Level 5 text};
coordinate (aux12) at ([xshift=5pt]s2211.east|-a11);
% auxuliary constructs for level 6
node[ntext] at (text4|-s)
  (text6) {Level 6 text};
coordinate (aux14) at ([xshift=5pt]s2211.east|-s);
% auxuliary constructs for level 7
node[ntext] at (text4|-s1)
  (text7) {Level 7 text};
coordinate (aux16) at ([xshift=5pt]s2211.east|-s1);
% auxuliary constructs for level 8
node[ntext] at (text4|-s11)
  (text8) {Level 8 text};
coordinate (aux18) at ([xshift=5pt]s2211.east|-s11);
% auxuliary constructs for level 9
node[ntext] at (text4|-s111)
  (text9) {Level 9 text};
coordinate (aux20) at ([xshift=5pt]s2211.east|-s111);
% auxuliary constructs for level 10
node[ntext] at (text4|-s1111)
  (text10) {Level 10 text};
coordinate (aux22) at ([xshift=5pt]s2211.east|-s1111);

begin{pgfonlayer}{background}
node[filling,fit=(text4) (aux2)] {};
node[filling,fit=(text3) (aux4)] {};
node[filling,fit=(text2) (aux6)] {};
node[filling,fit=(text1) (aux8)] {};
node[filling,fit=(text0) (aux10)] {};
node[filling,fit=(text5) (aux12)] {};
node[filling,fit=(text6) (aux14)] {};
node[filling,fit=(text7) (aux16)] {};
node[filling,fit=(text8) (aux18)] {};
node[filling,fit=(text9) (aux20)] {};
node[filling,fit=(text10) (aux22)] {};
end{pgfonlayer}
end{tikzpicture}
caption{The alarms Event Tree}
end{figure}
end{landscape}