TikZ diagram: how to make arrow like this

Question

How can i make arrows like this?

This is what I've done so far.

\documentclass[10pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[left=22mm,bottom=22mm,right=28mm,top=30mm]{geometry}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\begin{document}
\pagestyle{empty}

% Define block styles
\tikzstyle{decision} = [diamond, draw, fill=blue!20, 
    text width=4.5em, text badly centered, node distance=3cm, inner sep=0pt]
\tikzstyle{block} = [rectangle, draw, fill=blue!20, 
    text width=2cm, text centered, rounded corners, minimum height=10mm]
\tikzstyle{line} = [draw, -latex']
\tikzstyle{cloud} = [draw, ellipse,fill=red!20, node distance=3cm,
    minimum height=2em]
\begin{center}
\begin{tikzpicture}[node distance = 3.4cm, auto]

 \node  [block,yshift=30mm] (1) {1};
      \node [block, xshift=-30mm] (2) {2};
      \node[block, xshift=-60mm] (3) {3};
\node [block, xshift=-90mm] (4) {4};
        \node [block, xshift=-120mm] (5) {5};

       \node [block,yshift=30mm, xshift=-45mm] (6) {6};
         \node [block,yshift=-40mm, xshift=-105mm] (7) {7};
     \node [block,yshift=-60mm, xshift=-105mm] (8) {8};
             \node [block,yshift=-25mm, xshift=-75mm] (9) {9};
\node[block, xshift=-60mm,yshift=-60mm] (10) {10};
\node [block, xshift=-30mm,yshift=-60mm] (11) {11};
\node[block, xshift=0mm,yshift=-60mm] (12) {12};

\draw[->,>=latex'] (4) -- (3);
\draw[->,>=latex'] (3) -- (2);

\end{tikzpicture}
\end{center}
\end{document}

Answer 1

A bit of a miscellany ...

\documentclass[border=10pt,x11names,svgnames,dvipsnames]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,shadows.blur}% arrows is deprecated ; shapes would be better loaded with the required suffixes
\begin{document}
\tikzset{% \tikzstyle is deprecated
  block/.style={draw, top color=white!90!#1, bottom color=#1, shading angle=45, text width=2cm, text centered, rounded corners, minimum height=10mm},
}
\begin{tikzpicture} [node distance = 3.4cm, >=Latex, thick, draw=darkgray, every node/.append style={blur shadow}]
  \node [block=Crimson, text=white, yshift=30mm] (1) {1};
  \node [block=gray!40, xshift=-30mm] (2) {2};
  \node [block=green!25, xshift=-60mm] (3) {3};
  \node [block=magenta!25, xshift=-90mm] (4) {4};
  \node [block=yellow!30, xshift=-120mm] (5) {5};

  \node [block=DodgerBlue3, text=white, yshift=30mm, xshift=-45mm] (6) {6};
  \node [block=yellow!30, yshift=-40mm, xshift=-105mm] (7) {7};
  \node [block=magenta!25, yshift=-60mm, xshift=-105mm] (8) {8};
  \node [block=DodgerBlue3, text=white, yshift=-25mm, xshift=-75mm] (9) {9};
  \node [block=green!25, xshift=-60mm,yshift=-60mm] (10) {10};
  \node [block=Purple3!75!Periwinkle, text=white, xshift=-30mm,yshift=-60mm] (11) {11};
  \node [block=green!25, xshift=0mm,yshift=-60mm] (12) {12};

  \begin{scope}[every node/.append style={circle, draw=darkgray, anchor=center, fill=white, inner sep=1pt}, draw=darkgray, every edge/.append style={->, draw}]
    \path
    (5) edge coordinate [pos=.4] (a) (4)
    (4) edge coordinate [pos=.4] (b) (3)
    (3) edge coordinate [pos=.4] (c) (2)
    (a) edge (7)
    (12) edge (11)
    (11) edge (10)
    (10) edge coordinate [pos=.2] (d)  (8)
    (8) edge (7)
    (d) edge (9.south -| d)
    (b) edge (9.north -| b)
    (c) edge (6.south -| c)
    (2) -- (2 -| 1) coordinate [pos=.2] (e) node [pos=1, anchor=center] (f) {+}
    ;
    \path [every edge/.append style={<-}]
    (f) edge (1) edge (2);
    \path (12) edge (f);
    \draw [->] (e) |- (6);
    \draw [->] (e) |- (9);
    \foreach \i in {a,...,e} \node at (\i) {};
  \end{scope}
\end{tikzpicture}
\end{document}